Unmasking endotoxins in solution

ABSTRACT

The invention relates to unmasking endotoxins in compositions so that previously present, but undetectable endotoxins are rendered detectable.

This application is a divisional of U.S. patent application Ser. No.15/316,884, filed Dec. 7, 2016, which is a national phase applicationunder 35 U.S.C. § 371 of International Application No.PCT/EP2015/063152, filed Jun. 12, 2015, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/011,868, filed Jun. 13, 2014,and claims the benefit of European Patent Application No. 14172158.9,filed Jun. 12, 2014. The entirety of each of the above-referenceddisclosures are incorporated herein by reference.

The present invention relates to unmasking endotoxins in compositions,preferably pharmaceutical compositions, so that present but undetectableendotoxins are rendered detectable. Specifically, the invention relatesto a method of unmasking an endotoxin in a composition. The inventionfurther relates to a method of detecting an endotoxin in a composition.The invention further relates to a kit for unmasking an endotoxin in acomposition. The invention further relates to the use of a modulatorcapable of unmasking an endotoxin, e.g. by releasing an endotoxin from acomplex between said endotoxin and an endotoxin masker, to unmask anendotoxin in a composition.

BACKGROUND OF THE INVENTION

Endotoxins are part of the outer membrane of the cell wall ofGram-negative bacteria. Endotoxin is invariably associated withGram-negative bacteria regardless of whether the organisms arepathogenic or not. Although the term “endotoxin” is occasionally used torefer to any cell-associated bacterial toxin, in bacteriology it isproperly reserved to refer to the lipopolysaccharide (LPS) complexassociated with the outer membrane of Gram-negative pathogens such asEscherichia coli, Salmonella, Shigella, Pseudomonas, Neisseria,Haemophilus influenzae, Bordetella pertussis and Vibrio cholerae.

The presence of endotoxins in aqueous compositions is an intractableproblem which severely threatens and/or limits the application of manycompositions, in particular if intended for pharmaceutical use. This isespecially true of compositions comprising protein products, e.g.recombinant protein products. Naturally occurring endotoxins, especiallyendotoxins belonging to the class of compounds characterized aslipopolysaccharides (LPS) are molecules produced by certain types ofbacteria, for example gram-negative bacteria. Generally, endotoxins suchas LPS comprise an extended polysaccharide 0-antigen, a core antigenpolysaccharide including an outer core component and an inner corecomponent, and a lipid A domain comprising aliphatic amides andaliphatic acid esters. Such endotoxins are found in the outer membraneof gram-negative bacteria, where they contribute to bacterial structuralintegrity by shielding the organism from chemical attack. Suchendotoxins increase the negative charge of the cell membrane of thesebacteria, and help to stabilize the overall membrane structure. Suchendotoxins elicit strong responses from normal animal, e.g. human,immune systems because normal serum contains lipooligosaccharide (LOS)receptors which normally direct the cytotoxic effects of the immunesystem against invading bacterial pathogens bearing such endotoxins.

When present in the human blood in a form disassociated from theirsource bacteria, endotoxins such as LPS can cause endotoxemia which insevere cases can lead to septic shock. This reaction is due to theendotoxin lipid A component, which can cause uncontrolled activation ofthe mammalian immune system, in some instances producing inflammatorymediators such as toll-like receptor (TLR) 4, which is responsible forimmune system cell activation.

Bacteria, as well as the endotoxins they produce, are also ubiquitous.For instance, endotoxin contaminants are known to exist in the pipes andhoses of water supply systems, including those of laboratories andfacilities for preparing pharmaceutical formulations. The surfaces ofcontainers such as fermentors and glassware used in the process offormulating pharmaceuticals are also commonly contaminated. In addition,as humans carry bacteria and therefore endotoxins on their bodies, sothe staff of such facilities in which pharmaceuticals are formulatedalso represent a possible source of endotoxin contaminants.

Of course, in addition to the above, gram-negative bacteria themselvesfind wide use in the production of i.a. recombinant therapeuticproteins, so there is always a danger that endotoxin contamination ofaqueous compositions, e.g. pharmaceutical formulations, containing suchtherapeutic proteins may also arise directly from such bacteria used inthe production process.

To safeguard against potentially hazardous incorporation of endotoxincontaminants, whatever their source, measures must normally be taken toexclude endotoxin from all steps and products used in the productionprocess of such proteins before such solutions may be administered fortherapeutic purposes. In fact, the exclusion and/or removal andverifiable absence of all traces of (detectable) endotoxin are among therequirements which much must be met when seeking regulatory approval forany new therapeutic, in particular those containing products produced inbacteria, or which have come into contact with bacteria at any point inthe production process (see e.g. EMEA, Q6B, Specifications: TestProcedures and Acceptance Criteria for Biotechnological/BiologicalProducts; 2.1.4 Purity, Impurities and Contaminants; Contaminants; 4.1.3Purity and impurities; 2) FDA, Q6B, Specifications: Test Procedures andAcceptance Criteria for Biotechnological/Biological Products; II.A.4.Purity, Impurities and Contaminants; IV.A.3. Purity and Impurities). Forinstance, all containers holding and/or transferring solutions intendedfor eventual administration must be rendered endotoxin-free prior tocontact with the solution. A depyrogenation oven is used for thispurpose, in which temperatures in excess of 200° C. are required tobreak down endotoxins. Based on primary packaging material as syringesor vials, a glass temperature of 250° C. and a holding time of 30minutes is typical to achieve a reduction of endotoxin levels by afactor of 1000. Usually, liquids cannot be depyrogenated by heat,therefore different methods are used, such as chromatography (e.g. anionexchange), phase extraction (e.g. Trition X-114), filtration (e.g.ultrafiltration).

One common assay for detecting the activity of endotoxin is the limulusamebocyte lysate (LAL) assay, which utilizes blood from the horseshoecrab. Very low levels of endotoxin can cause coagulation by the limuluslysate due to a powerful amplification through an enzyme cascade.However, due to the dwindling population of horseshoe crabs, effortshave been made to develop alternative, e.g. recombinant, Factor C assaysfor detecting the presence of endotoxin in solution. The most promisingof such methods are enzyme-linked affinitysorbent assays, using a solidphase for endotoxin capturing and subsequent detection by recombinantversion of a protein in the LAL assay, Factor C. The EndoLISA® kit isone such affinitysorbent assay.

However, even the best available tests for detecting the presence ofpyrogens, such as endotoxin, in particular LPS, are often unable todetect LPS in solution. This implies the danger that solutions which arereasonably—in the absence of any detectable endotoxin—thought to beendotoxin-free in fact contain endotoxin which is simply masked so as tobe rendered undetectable. Such solutions, e.g. pharmaceuticalformulations will not be barred from regulatory approval (at least notdue to containing endotoxin), because by all diagnostic appearances,these solutions are endotoxin-free, therefore fulfilling—or at leastappearing to fulfill—this regulatory requirement. Clearly, however,administration of such ostensibly endotoxin-free solutions to subjectsrisks triggering the types of reactions mentioned above. In suchinstances, one may learn of the presence of masked endotoxin in suchsolutions too late, after subjects have already developed the types ofadverse and potentially life-threatening reactions described above. Inaddition, from a hygenic standpoint, drug regulatory authorities placegreat value on positively knowing which substances are contained inpharmaceutical compositions and which are not. This ultimately comesdown to the ability to reliably detect all components in a givencomposition, and one's ability to believe the results obtained inreference to both the presence and absence of all substances tested.

It should be noted that the terms “masking” and “unmasking”, as pertainto endotoxins, have been used with various meanings in the literature.On the one hand, the literature uses the term “endotoxin unmasking” or“endotoxin demasking” to describe removal of endotoxin from certainsolutions (e.g. protein solutions). In this case, a certain endotoxincontent is detectable before and after using common procedures forendotoxin removal (e.g. chromatography). Where the available techniquesare inadequate for complete removal of endotoxin from the particularsample, the endotoxin which cannot be removed is referred to as “masked”endotoxin; any endotoxin which can be removed by available techniques isreferred to as “unmasked” or “demasked” endotoxin. According to thisusage of the term, “masked” endotoxin thus denotes endotoxin whichcannot be removed, and implies insufficient removal of (detectable)endotoxin.

On the other hand, the literature also uses the term “endotoxin masking”in the case of inadequate endotoxin detection. In this case, only afractional amount or, in many cases, no endotoxin whatsoever can bedetected, although endotoxin is present. According to this usage of theterm, “masked” endotoxin thus denotes endotoxin which cannot bedetected, or can only barely be detected, and implies insufficientendotoxin detection.

Inadequate detection of endotoxin can occur in various compositions. Forexample in protein solutions (Petsch et al., Analytical Biochemistry259, 42-47, 1998), drug products (J. Chen and K. Williams, Follow-Up onLow Endotoxin Recovery in Biologics PDA Letter, October 2013), or evenin common formulation components of drug products (J. Reich et al.,Poster: Low Endotoxin Recovery in Common Protein Formulations, 6thWorkshop on Monoclonal Antibodies, Basel, Switzerland, 2013; J. Reich etal., Poster: Low Endotoxin Recovery in Biologics: Case Study—Comparisonof Natural Occurring Endotoxin (NOE) and Commercially Available StandardEndotoxin, PDA Annual meeting, San Antonio, USA, 2014).

WO 2009/152384 A1 discloses notional compositions by defining categoriesof components in the compositions and then providing lists of componentswithin each category. This document does not disclose any individualizedcomposition comprising a protein, a C8-C16 alkanol and LPS.

Similarly, WO 02/057789 A2 discloses notional compositions by definingcategories of components in the compositions and then providing lists ofcomponents within each category. This document does not disclose anyindividualized composition comprising a protein, a C8-C16 alkanol andLPS.

EP 1 917 976 A1 discloses certain compositions, but does not discloseany composition comprising a protein, a C8-C16 alkanol and LPS.

There thus exists a strong motivation to provide ways in which allendotoxin present in compositions, including endotoxin which isundetectable because it is being masked by certain other compositioncomponents, may be unmasked such that it is rendered detectable.Providing a way to unmask and/or detect hitherto undetectable endotoxinin a composition would greatly assist in promoting patient safety. It isan aim of the present invention to address such needs.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to an aqueous composition comprising aprotein and an aliphatic compound with C₈-C₁₆ as the main chain andwhich compound preferably has a substitution by one or more heteroatoms.

The aqueous composition may preferably be a pharmaceutical compositioncontaining a protein to which the aliphatic compound is added. Theaddition of the aliphatic compound helps to improve the detectability ofa potential contamination of the composition by an LPS. As stated inother parts of this application, LPS might escape detection byconventional endotoxin tests because of being masked by someconstituents of protein-containing compositions.

According to a preferred embodiment, the aliphatic compound is abranched compound with at least one substitution in the main chainwherein the substitution may be selected from methyl, ethyl, propyl andbutyl groups.

The main chain of the aliphatic compound is as defined elsewhere herein.

According to a further preferred embodiment, the main chain is selectedfrom a C₈-C₁₆ alkyl, C₈-C₁₆ alkenyl and C₈-C₁₆ alkynyl. The main chainmay contain one or more double bonds and/or one or more triple bonds,whereas a saturated alkyl chain is the more preferred embodiment.

According to a further preferred embodiment, the heteroatom that mayform part of the aliphatic compound is selected from O, S and N, whereasO is the more preferred substitution.

A further preferred aliphatic compound is selected from an alkanol,which is preferably an unbranched alkanol, more preferably a 1-alkanoland most preferably 1-dodecanol.

The aliphatic compound is assumed to stabilize a potentiallycontaminating LPS molecule in a form that renders LPS more susceptibleto detection by conventional endotoxin test kits such as the EndoLISA®by Hyglos GmbH.

Compositions that might be rendered more susceptible to the detection ofendotoxin often contain detergents which may be selected from an anionicdetergent, a cationic detergent, a nonionic detergent, an amphotericdetergent and any combination thereof. Preferred detergents that may beused in such compositions may be selected from: an anionic detergentwhich can be chosen from the group consisting of: alkyl sulfates,preferably ammonium lauryl sulfate or sodium lauryl sulfate (SDS);alkyl-ether sulfates, preferably sodium laureth sulfate or sodium myrethsulfate; cholesterol sulfate; sulfonates, preferablydodecylbenzensulfonate, sodiumlauryl sulfoacetate or xylene sulfonate;alkyl sulfo succinates, preferably disodium lauryl sulfosuccinate;sulfoxides, preferably dodecyl methyl sulfoxide; phosphates, preferablytrilaureth-4 phosphate; and carboxylates, preferably sodium stearate orsodium lauroyl sarcosinate;

a cationic detergent which can be chosen from the group consisting of:primary amines; secondary amines; tertiary amines; and quaternaryammonium cations such as alkyltrimethylammonium salts (preferably cetyltrimethylammonium bromide (CTAB); or cetyl trimethylammonium chloride(CTAC)); cetylpyridinium chloride (CPC); quaternary ammonium detergents,preferably tris[2-(2-hydroxyethoxy)ethyl]-octadecyl-ammonium phosphate(Quaternium 52); and hydroxyethylcellulose ethoxylate, quaternized(Polyquaternium-10);

a nonionic detergent which can be chosen from the group consisting of:polyoxyethylene glycol sorbitan alkyl esters (polysorbates), preferablypolysorbate 20 (TWEEN™-20), polysorbate 40, polysorbate 60 orpolysorbate 80 (TWEEN™-80); polyoxyethylene glycol alkyl ethers;polyoxypropylene glycol alkyl ethers; glucoside alkyl ethers;polyoxyethylene glycol octylphenol ethers; polyoxyethylene glycolalkylphenol ethers; glycerol alkyl esters; sorbitan alkyl esters; blockcopolymers of polyethylene glycol and polypropylene glycol; cocamideMEA; sterols, preferably cholesterol; cyclodextrins; poloxamers,preferably Pluronic block polymers; and cocamide DEA;

an amphoteric detergent which can be chosen from the group consistingof: CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate);sultaines, preferably cocamidopropyl hydroxysultaine; betaines,preferably cocamidopropyl betaine; amino oxides, preferably palmitamineoxide, laurylamine oxide and amine oxide of general formula R³N+O⁻,wherein R³ is C₈-C₁₈ alkyl, C₈-C₁₈ alkenyl, or C₈-C₁₈ alkynyl; andlecithin.

According to a further preferred embodiment, the detergent is selectedfrom a polysorbate, preferably Polysorbate 20 and Polysorbate 80, apoloxamer, preferably Poloxamer 188, an octoxynol, preferably anOctoxynol 9, an alkylamine oxide, preferably laurylamine oxide, aquaternary ammonium salt, preferablytris[2-(2-hydroxyethoxy)ethyl]-octadecyl-ammonium phosphate, an alkylphosphate, preferably trilaureth-4 phosphate, and a stearate, preferablysodium stearate.

In a preferred aqueous composition, the protein is chosen from anantibody, an antibody fragment, a hormone, an enzyme, a fusion protein,a protein conjugate and any combination thereof, which proteins arefrequently used as the active agent of pharmaceutical preparations wherespecific care must be taken that LPS does not remain undetected in thequality control of pharmaceuticals.

In a further preferred embodiment, the antibody fragment is selectedfrom a Fab, a Fab′, a F(ab′)2 and an Fv, a single chain antibody and anycombination thereof.

In a further preferred embodiment, the aqueous composition, in additionto the active pharmaceutical ingredient, which may be the proteinmentioned above, may contain an additional protein selected from analbumin, which is preferably human serum albumin, bovine serum albuminand/or ovalbumin. The further protein may be of assistance in renderinga potential LPS contamination more detectable by conventional endotoxintests such as the ones mentioned above.

In a further preferred embodiment, the aqueous composition may comprisea chaotropic agent, a cation or a combination thereof. The sameingredients also can help to bring a potential LPS contamination into aform that is more susceptible to detection by an endotoxin test byHyglos GmbH.

According to a further preferred embodiment, the chaotropic agent isselected from urea, guanidinium chloride, butanol, ethanol, lithiumperchlorate, lithium acetate, magnesium chloride, phenol, propanol andthiourea.

According to a further preferred embodiment, the cation is a divalentcation, preferably selected from Ca2+, Mg2+, Sr2+ and Zn2+.

According to a further preferred embodiment, the further protein, whichmay be an albumin, is present in a concentration in the range from0.1-20 mg/ml, preferably in the range from 1-10 mg/ml, more preferablyin an amount of 10 mg/ml.

In a further preferred embodiment, the aliphatic compound is present inthe concentration from 0.01-100 mM, preferably in a concentration from0.1-10 mM. This concentration range is in particular preferred for an1-alkanol, preferably 1-dodecanol.

In a further preferred embodiment, the detergent is present in aconcentration from 0.001-1.0 wt %, preferably 0.05-0.5 wt %, preferablyfrom 0.02-0.2 wt %.

In a further preferred embodiment, the chaotopic agent is present in aconcentration from 1 mM-1 M, preferably from 25-200 mM, preferably from10 mM-100 mM.

In a further preferred embodiment, the divalent cation is present in aconcentration from 1-400 mM, preferably in a concentration from 10-200mM, more preferably in a concentration from 50-100 mM.

In a further preferred embodiment, the pH of the composition is in therange from 2-12, preferably in the range from pH 5-10.

In a further preferred embodiment, the composition contains Factor Cprotein, which is a component used in for conventional endotoxin assays.

In a preferred embodiment, the Factor C protein is a recombinant FactorC protein.

A very preferred aqueous composition comprises a protein, preferably anantibody, in combination with a 1-alkanol, preferably 1-dodecanol in aconcentration range from 0.1-10 mM, a detergent of claim 8 in aconcentration range from 0.002-0.2 wt %, a divalent cation, preferablyCa2+, in a concentration range from 10-200 mM, and a pH from 5 to 10.

A further very preferred aqueous composition is as set out above in theimmediately preceding paragraph, and further comprising a chaotropicagent, preferably guanidinium chloride, in the concentration range from10 mM-100 mM.

In the above compositions, LPS, if present, will be susceptible todetection by conventional endotoxin assays such as the EndoLisa ofHyglos GmbH.

One disclosure relates to a method of unmasking an endotoxin in acomposition, preferably a pharmaceutical composition, comprising anendotoxin masker and suspected of comprising said endotoxin, said methodcomprising the step of adding to said composition a modulator capableunmasking said endotoxin, e.g. by of releasing said endotoxin, ifpresent, from a complex between said endotoxin and said endotoxinmasker. The pharmaceutical composition will in most cases be an aqueouscomposition.

A further disclosure relates to a method of detecting an endotoxin in acomposition, preferably a pharmaceutical composition, comprising anendotoxin masker and suspected of comprising said endotoxin, said methodcomprising the steps of adding to said composition a modulator capableof unmasking said endotoxin, e.g. by releasing said endotoxin, ifpresent, from a complex between said endotoxin and said endotoxinmasker; and detecting said endotoxin by means of a detection method. Thepharmaceutical composition will in most cases be an aqueous composition.

In certain embodiments, the above methods of unmasking and/or detectingmay further comprise the step of adding to said composition an agentwhich influences hydrogen bonding stability in solution. In certainembodiments, it is preferable to add said agent which influenceshydrogen bonding stability in solution to said solution prior to theaddition of said modulator.

A further disclosure relates to a kit for unmasking an endotoxin in acomposition, preferably a pharmaceutical composition, comprising anendotoxin masker and suspected of comprising said endotoxin, said kitcomprising a) a modulator capable of unmasking said endotoxin, e.g. byreleasing said endotoxin from a complex between said endotoxin and saidendotoxin masker; and b) an agent which influences hydrogen bondingstability in solution; wherein components (a) and (b) are in same ordifferent packages.

A further disclosure relates to a use of a modulator capable ofunmasking endotoxin, e.g. by releasing an endotoxin from a complexbetween said endotoxin and an endotoxin masker, to unmask an endotoxinin a composition, preferably a pharmaceutical composition suspected ofcomprising said endotoxin and said endotoxin masker.

Other embodiments of this invention will be readily apparent from thefollowing disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a mechanism assumed to underlie the unmasking ofendotoxin according to an embodiment of the present invention. In thescenario depicted in FIG. 1, the endotoxin is present in solution with adetergent (capable of acting as an endotoxin masker), which formsdetergent micelles in which endotoxin is embedded and thus masked fromdetection. FIG. 1 schematically shows the effects of adding asingle-component modulator which breaks up these micelles, liberatingembedded endotoxin, while not forming new micelles of its own. Followingbreakup of the detergent micelles, the single-component modulator thenserves as a chaperone to the liberated endotoxin, stabilizing it insolution. An equilibrium exists between individual and aggregatedendotoxin moieties, and the detection of the endotoxin aggregateproceeds based on the aggregated form (“Aggregates are the biologicallyactive units of endotoxins”. Mueller, M., Lindner, B., Kusomoto, S.,Fukase, K., Schromm, A. B. and Seydel, U. (2004) The Journal ofBiological Chemistry, Vol. 279, No. 25, pp. 26307-26313. Endotoxin inthe form shown in panel (a) is not susceptible to detection, whereasendotoxin in the form shown in panel (c) is detectable. The scenariodepicted in FIG. 1 is discussed in further detail below.

FIG. 2 illustrates a mechanism assumed to underlie the unmasking ofendotoxin according to a further embodiment of the present invention. Inthe scenario depicted in FIG. 2, the endotoxin is present in solutionwith a detergent (capable of acting as an endotoxin masker), which formsdetergent micelles in which endotoxin is embedded and thus masked fromdetection. FIG. 2 schematically shows the effects of adding adual-component modulator comprising protein and non-protein components.This dual-component modulator is assumed to break apart the detergentmicelle in which the endotoxin was previously inserted and masked. Thenon-protein component of the modulator transiently stabilizes theendotoxin outside of the detergent micelle, while the protein componentof the modulator destabilizes the detergent micelle by binding i.a.molecules of detergent. The scenario depicted in FIG. 2 is discussed infurther detail below.

FIG. 3 illustrates a mechanism assumed to underlie the unmasking ofendotoxin according to a further embodiment of the present invention. Inthe scenario depicted in FIG. 3, the endotoxin is present in solutionwith a detergent (capable of acting as an endotoxin masker), which formsdetergent micelles in which endotoxin is embedded and thus masked fromdetection. FIG. 3 schematically shows the effects of adding amultiple-component modulator, as well as an agent influencing hydrogenbonding stability. Together, the multiple-component modulator and theagent influencing hydrogen bonding stability destabilize the detergentmicelle initially masking the endotoxin, and promote endotoxinaggregation such that it is rendered detectable. The scenario depictedin FIG. 3 is discussed in further detail below.

FIG. 4 illustrates a mechanism assumed to underlie the unmasking ofendotoxin according to a further embodiment of the present invention. Inthe scenario depicted in FIG. 4, the endotoxin is present in solution,i.a. with a protein. The protein comprises a binding cleft in whichendotoxin may stably bind and thus remain masked from detection. FIG. 4schematically shows the effects of adding a multiple-component modulatorsuch that the previously masked endotoxin aggregates and is rendereddetectable. The scenario depicted in FIG. 4 is discussed in furtherdetail below.

FIG. 5 illustrates a mechanism assumed to underlie the unmasking ofendotoxin according to a further embodiment of the present invention. Inthe scenario depicted in FIG. 5, the endotoxin is present in solutionwith a protein (capable of acting as an endotoxin masker). The proteincomprises a binding cleft in which endotoxin may stably bind and thusremain masked from detection. FIG. 5 schematically shows the effects ofadding an agent influencing hydrogen bonding stability as well as amultiple-component modulator including protein and non-proteincomponents. Together, these destabilize the endotoxin in its complexwith the masking protein, transiently stabilize endotoxin outside of thecomplex with the masking protein, and promote aggregation of theliberated endotoxin, rendering it detectable. The scenario depicted inFIG. 5 is discussed in further detail below.

FIG. 6 illustrates a mechanism assumed to underlie the unmasking ofendotoxin according to a further embodiment of the present invention. Inthe scenario depicted in FIG. 6, the endotoxin is present in solutionwith a protein as well as with a detergent (capable of acting as anendotoxin masker). The protein comprises a binding cleft in whichendotoxin may stably bind and thus remain masked from detection. Inaddition, the detergent forms stable micelles in which molecules ofendotoxin stably inserted are masked. FIG. 6 schematically shows theeffects of adding an agent influencing hydrogen bonding stability aswell as a multiple-component modulator including protein and non-proteincomponents. Together, these destabilize the endotoxin in its complexwith the masking protein and/or in the masking detergent micelle,transiently stabilize endotoxin outside of the complex with the maskingprotein and/or in the masking detergent micelle, and promote aggregationof the liberated endotoxin, rendering it detectable. The scenariodepicted in FIG. 6 is discussed in further detail below.

FIG. 7 is a graph showing the percent recovery of the endotoxin LPS froma detergent masker (polysorbate 20/citrate) using modulator systems of1-dodecanol alone, and 1-dodecanol together with BSA.

FIG. 8 is a graph showing the percent recovery of the endotoxin LPS fromthe detergent masker TRITON™ (non-ionic surfactant) X-100 using variousmodulator systems of various strengths.

FIG. 9 is a graph showing the percent recovery of the endotoxin LPS fromvarious detergent masking systems using a variety of modulator systems.

FIG. 10 is a graph showing the percent recovery of the endotoxin LPSfrom a masking detergent (polysorbate 20) as dependent on pH.

FIG. 11 is a graph showing the percent recovery of the endotoxin LPSfrom a masking detergent (polysorbate 80) as dependent on pH.

FIG. 12 is a flowchart showing a generalized validation scheme fordetermining and optimizing an unmasking process for a composition inquestion suspected of containing masked endotoxin.

FIG. 13 is a table showing a generalized evaluation scheme fordetermining and optimizing an unmasking process for a composition inquestion suspected of containing masked endotoxin.

FIG. 14 is a general schematic representation of the inventive methodsherein, as viewed from the standpoint of the level of LPS recovery (i.e.measured LPS activity) before and after masking (left and middle bars offigure, respectively), as well as after unmasking according to themethods of the present invention (right bar of figure). The left andmiddle bars of the figure thus represent the circumstances commonlyprevailing in pharmaceutical formulations, in which endotoxin which ispresent in solution, is rendered undetectable by one or more endotoxinmaskers. This endotoxin can be again rendered detectable, i.e. can be“rescued” out of its masked state, by the methods of the presentinvention, enabling one to detect the previously masked endotoxin.

FIG. 15 shows a generic diagram illustrating the dynamics associatedwith the unmasking methods described herein. The transition from active(i.e. aggregated and therefore detectable) LPS at the far left to maskedLPS (middle bottom; non-aggregated) is shown for several representativeendotoxins. Because the energy associated with the “masked LPS” is lowerthan that associated with “active LPS”, the LPS remains stabilized inthis masked form. The inventive methods described herein effectivelydestabilize this masked LPS, thus raising its energy to a level abovethat of masked LPS, from where LPS can again fall back down in energyinto aggregated form (far right of diagram). It as assumed that thereconfiguring modulator plays a key role in mediating this rescue of LPSfrom solubilized (masked) to aggregate (unmasked) form.

GENERAL

It is to be understood that the foregoing general description as well asthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed. In thisapplication, the use of the singular includes the plural unlessspecifically stated otherwise. In this application, the use of “or”means “and/or” unless stated otherwise. Further, the use of the term“including” as well as other grammatical forms such as “includes” and“included”, is not limiting. In the same sense, the use of the term“comprising” as well as other grammatical forms such as “comprises” and“comprised” is not limiting. Section headings throughout the descriptionare for organizational purposes only. They are in particular notintended as limiting for the various embodiments described therein, andit is to be understood that elements and embodiments described under onesubheading may be freely combined with elements and embodimentsdescribed under another subheading.

In the foregoing, subsequent description the claims, the features of anyone embodiment are intended as being combinable with those of any otherembodiment. Such combinations of one or more features in any oneembodiment with one or more features in any other embodiment belong tothe disclosure of the present application as filed.

All documents or portions of documents cited in this application,including but not limited to patents, patent applications, articles,monographs, books, treaties and regulations, are hereby expresslyincorporated by reference in their entirety for any purpose.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an aqueous composition comprising aprotein and an aliphatic compound with C₈-C₁₆ as the main chain andwhich compound preferably has a substitution by one or more heteroatoms.

The aqueous composition may preferably be a pharmaceutical compositioncontaining a protein to which the aliphatic compound is added. Theaddition of the aliphatic compound helps to improve the detectability ofa potential contamination of the composition by an LPS. As stated inother parts of this application, LPS might escape detection byconventional endotoxin tests because of being masked by someconstituents of protein-containing compositions.

According to a preferred embodiment, the aliphatic compound is abranched compound with at least one substitution in the main chainwherein the substitution may be selected from methyl, ethyl, propyl andbutyl groups.

The main chain of the aliphatic compound is as defined elsewhere herein.

According to a further preferred embodiment, the main chain is selectedfrom a C₈-C₁₆ alkyl, C₈-C₁₆ alkenyl and C₈-C₁₆ alkynyl. The main chainmay contain one or more double bonds and/or one or more triple bonds,whereas a saturated alkyl chain is the more preferred embodiment.

According to a further preferred embodiment, the heteroatom that mayform part of the aliphatic compound is selected from O, S and N, whereasO is the more preferred substitution.

A further preferred aliphatic compound is selected from an alkanol,which is preferably an unbranched alkanol, more preferably a 1-alkanoland most preferably 1-dodecanol.

The aliphatic compound is assumed to stabilize a potentiallycontaminating LPS molecule in a form that renders LPS more susceptibleto detection by conventional endotoxin test kits such as the EndoLISA®by Hyglos GmbH.

Compositions that might be rendered more susceptible to the detection ofendotoxin often contain detergents which may be selected from an anionicdetergent, a cationic detergent, a nonionic detergent, an amphotericdetergent and any combination thereof. Preferred detergents that may beused in such compositions may be selected from: an anionic detergentwhich can be chosen from the group consisting of: alkyl sulfates,preferably ammonium lauryl sulfate or sodium lauryl sulfate (SDS);alkyl-ether sulfates, preferably sodium laureth sulfate or sodium myrethsulfate; cholesterol sulfate; sulfonates, preferablydodecylbenzensulfonate, sodiumlauryl sulfoacetate or xylene sulfonate;alkyl sulfo succinates, preferably disodium lauryl sulfosuccinate;sulfoxides, preferably dodecyl methyl sulfoxide; phosphates, preferablytrilaureth-4 phosphate; and carboxylates, preferably sodium stearate orsodium lauroyl sarcosinate;

a cationic detergent which can be chosen from the group consisting of:primary amines; secondary amines; tertiary amines; and quaternaryammonium cations such as alkyltrimethylammonium salts (preferably cetyltrimethylammonium bromide (CTAB); or cetyl trimethylammonium chloride(CTAC)); cetylpyridinium chloride (CPC); quaternary ammonium detergents,preferably tris[2-(2-hydroxyethoxy)ethyl]-octadecyl-ammonium phosphate(Quaternium 52); and hydroxyethylcellulose ethoxylate, quaternized(Polyquaternium-10);

a nonionic detergent which can be chosen from the group consisting of:polyoxyethylene glycol sorbitan alkyl esters (polysorbates), preferablypolysorbate 20 (TWEEN™-20), polysorbate 40, polysorbate 60 orpolysorbate 80 (TWEEN™-80); polyoxyethylene glycol alkyl ethers;polyoxypropylene glycol alkyl ethers; glucoside alkyl ethers;polyoxyethylene glycol octylphenol ethers; polyoxyethylene glycolalkylphenol ethers; glycerol alkyl esters; sorbitan alkyl esters; blockcopolymers of polyethylene glycol and polypropylene glycol; cocamideMEA; sterols, preferably cholesterol; cyclodextrins; poloxamers,preferably Pluronic block polymers; and cocamide DEA;

an amphoteric detergent which can be chosen from the group consistingof: CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate);sultaines, preferably cocamidopropyl hydroxysultaine; betaines,preferably cocamidopropyl betaine; amino oxides, preferably palmitamineoxide, laurylamine oxide and amine oxide of general formula R³N+O⁻,wherein R³ is C₈-C₁₈ alkyl, C₈-C₁₈ alkenyl, or C₈-C₁₈ alkynyl; andlecithin.

According to a further preferred embodiment, the detergent is selectedfrom a polysorbate, preferably Polysorbate 20 and Polysorbate 80, apoloxamer, preferably Poloxamer 188, an octoxynol, preferably anOctoxynol 9, an alkylamine oxide, preferably laurylamine oxide, aquaternary ammonium salt, preferablytris[2-(2-hydroxyethoxy)ethyl]-octadecyl-ammonium phosphate, an alkylphosphate, preferably trilaureth-4 phosphate, and a stearate, preferablysodium stearate.

In a preferred aqueous composition, the protein is chosen from anantibody, an antibody fragment, a hormone, an enzyme, a fusion protein,a protein conjugate and any combination thereof, which proteins arefrequently used as the active agent of pharmaceutical preparations wherespecific care must be taken that LPS does not remain undetected in thequality control of pharmaceuticals.

In a further preferred embodiment, the antibody fragment is selectedfrom a Fab, a Fab′, a F(ab′)2 and an Fv, a single chain antibody and anycombination thereof.

In a further preferred embodiment, the aqueous composition, in additionto the active pharmaceutical ingredient, which may be the proteinmentioned above, may contain an additional protein selected from analbumin, which is preferably human serum albumin, bovine serum albuminand/or ovalbumin. The further protein may be of assistance in renderinga potential LPS contamination more detectable by conventional endotoxintests such as the ones mentioned above.

In a further preferred embodiment, the aqueous composition may comprisea chaotropic agent, a cation or a combination thereof. The sameingredients also can help to bring a potential LPS contamination into aform that is more susceptible to detection by an endotoxin test byHyglos GmbH.

According to a further preferred embodiment, the chaotropic agent isselected from urea, guanidinium chloride, butanol, ethanol, lithiumperchlorate, lithium acetate, magnesium chloride, phenol, propanol andthiourea.

According to a further preferred embodiment, the cation is a divalentcation, preferably selected from Ca2+, Mg2+, Sr2+ and Zn2+.

According to a further preferred embodiment, the further protein, whichmay be an albumin, is present in a concentration in the range from0.1-20 mg/ml, preferably in the range from 1-10 mg/ml, more preferablyin an amount of 10 mg/ml.

In a further preferred embodiment, the aliphatic compound is present inthe concentration from 0.01-100 mM, preferably in a concentration from0.1-10 mM. This concentration range is in particular preferred for an1-alkanol, preferably 1-dodecanol.

In a further preferred embodiment, the detergent is present in aconcentration from 0.001-1.0 wt %, preferably 0.05-0.5 wt %, preferablyfrom 0.02-0.2 wt %.

In a further preferred embodiment, the chaotopic agent is present in aconcentration from 1 mM-1 M, preferably from 25-200 mM, preferably from10 mM-100 mM.

In a further preferred embodiment, the divalent cation is present in aconcentration from 1-400 mM, preferably in a concentration from 10-200mM, more preferably in a concentration from 50-100 mM.

In a further preferred embodiment, the pH of the composition is in therange from 2-12, preferably in the range from pH 5-10.

In a further preferred embodiment, the composition contains Factor Cprotein, which is a component used in for conventional endotoxin assays.

In a preferred embodiment, the Factor C protein is a recombinant FactorC protein.

A very preferred aqueous composition comprises a protein, preferably anantibody, in combination with a 1-alkanol, preferably 1-dodecanol in aconcentration range from 0.1-10 mM, a detergent of claim 8 in aconcentration range from 0.002-0.2 wt %, a divalent cation, preferablyCa2+, in a concentration range from 10-200 mM, and a pH from 5 to 10.

A further very preferred aqueous composition is as set out above in theimmediately preceding paragraph, and further comprising a chaotropicagent, preferably guanidinium chloride, in the concentration range from10 mM-100 mM.

In the above compositions, LPS, if present, will be susceptible todetection by conventional endotoxin assays such as the EndoLisa ofHyglos GmbH.

As mentioned above, one disclosure relates to a method of unmasking anendotoxin in a composition, preferably a pharmaceutical composition,comprising an endotoxin masker and suspected of comprising saidendotoxin, said method comprising the step of adding to said compositiona modulator capable of unmasking said endotoxin, e.g. by releasing saidendotoxin, if present, from a complex between said endotoxin and saidendotoxin masker. The pharmaceutical composition will in most cases bean aqueous composition.

A further disclosure relates to a method of detecting an endotoxin in acomposition, preferably a pharmaceutical composition, comprising anendotoxin masker and suspected of comprising said endotoxin, said methodcomprising the steps of: adding to said composition a modulator capableof unmasking said endotoxin, e.g. by releasing said endotoxin, ifpresent, from a complex between said endotoxin and said endotoxinmasker; and detecting said endotoxin by means of a detection method. Thepharmaceutical composition will in most cases be an aqueous composition.

Endotoxin

The term “endotoxin” refers to a molecule produced on the surface ofbacteria in particular gram-negative bacteria, that is bacteria which,because of their thin peptidoglycan layer sandwiched between an innercell membrane and a bacterial outer membrane, do not retain the crystalviolet stain used in the Gram staining method of bacterialdifferentiation and therefore evade positive detection by this method.Specifically, endotoxins are biologically active substances present inthe outer membrane of gram-negative bacteria. One common class ofendotoxins is lipopolysaccharides (LPS). For the purposes of the presentapplication, the terms “endotoxin” and “LPS” are used interchangeably.As is discussed elsewhere herein, however, it is understood that thereexist different types of LPS, e.g. derived from different sources, andthat the terms “endotoxin” and “LPS” are intended to encompass thesedifferent types of LPS. Endotoxins are located on the surface ofbacteria and, together with proteins and phospholipids, form the outerbacterial membrane. Generally, LPS is made up of two parts withdifferent chemical and physical properties; a hydrophilic sugar domain(the polysaccharide) and a hydrophobic lipid domain (lipid A). Twodistinct regions can be recognized in the polysaccharide: the coreoligosaccharide and the O-specific polysaccharide (M. A. Freudenberg, C.Galanos, Bacterial Lipopolysaccharides: Structure, Metabolism andMechanisms of Action, Intern. Rev. Immunol. 6, 1990).

The lipid A is highly hydrophobic and is the endotoxically active partof the molecule. Lipid A is typically composed of abeta-D-GlcN-(1-6)-alpha-D-GlcN disaccharide carrying two phosphorylgroups. Up to four acyl chains are attached to this structure. Thesechains can then in turn be substituted by further fatty acids, which canvary quite considerably between species in their nature, number, length,order and saturation. Covalently attached to the lipid A is the coresection of the molecule which can itself be formally divided into innerand outer core. The inner core is proximal to the lipid A and containsunusual sugars like 3-deoxy-D-manno-octulosonic acid (KDO). The outercore extends further from the bacterial surface and is more likely toconsist of more common sugars such as hexoses and hexosamines. Onto thisis attached, in most cases, a polymer of repeating saccharide subunitscalled the O-polysaccharide, also typically composed of common sugars.This O-polysaccharide is not ubiquitous, however, as it is seen to betruncated or lacking in a number of Gram-negative strains. In addition,certain strains carry mutations in the otherwise well-conserved locusand are termed “rough mutants” to differentiate them from the wild-type“smooth” strains which express O-polysaccharide bearing LPS (C. Erridge,E. Bennett-Guerrero, I. Poxton, Structure and function oflipopolysaccharides, Microbes and Infection, 2002). Copious informationrelating to endotoxins, e.g. LPS, as well as their impact on health maybe found in the book “Endotoxin in Health and Disease”, edited by HelmutBrade, Steven M. Opal, Stefanie N. Vogel and David C. Morrison, 1999,published by Marcel Dekker, Inc., ISBN 0-8247-1944-1.

As mentioned above, endotoxin may derive from different bacterialsources. The chemical nature of endotoxin may vary slightly from sourceto source. For instance, endotoxins derived from different bacterialsources may differ slightly in the length of the aliphatic chains in thealiphatic amides and aliphatic acid esters of the lipid A domain.However, despite slight variations in endotoxin structure from source tosource, the same basic structure as described herein above applies formost if not all endotoxins, implying a similar mode of action, and acorrespondingly similar mode of influencing endotoxin behaviorregardless of the bacterial species of origin. Examples of knownendotoxins include those derived from e.g. E. coli, e.g. E. coli 055:65(such as available from Sigma as product number L2637-5MG) or E. coli K12; S. abortus equi (such as available from Acila as product number1220302); Klebsiella pneumonia; Morganella morganii; Yersiniaenterocolitica; Serratia marcescens; Neisseria, e.g. Neisseriameningitis; Acinetobacter baumanni; Enterobacter cloacae, e.g. naturallyoccurring endotoxin (NOE); Pseudomonas, e.g. Pseudomonas aeruginosa;Salmonella, e.g. Salmonella enteric; Shigella; Haemophilus influenza;Bordatella pertussis; and Vibrio cholerae. It is to be understood thatthis list is merely exemplary and in no way restricts the term“endotoxin” as used herein.

Endotoxin Masker

The term “endotoxin masker” refers to a substance which, in solutionwith the endotoxin, renders the endotoxin undetectable by availabledetection methods, e.g. by limulus amebocyte lysate (LAL) tests.Typically, endotoxin is detectable when it exists in solution inaggregated form, i.e. in a form in which multiple, or least twoendotoxin moieties are held together in spatial proximity bynon-covalent interactions such as electrostatic interactions,hydrophobic interactions, Van der Waals interactions or any combinationthereof. However, endotoxin becomes significantly less active(undetectable) as measured by common detection systems, i.e. is masked,when its active aggregation state is changed such that the endotoxinbecomes solubilized as individual molecules of endotoxin. It can beassumed that discrete molecular entities of endotoxin are stabilized,for example, by detergents present in the solution. Such detergents areassumed to stabilize individual endotoxin moieties by forming detergentmicelles in which the individual endotoxin moieties become embedded andare no longer capable of reacting with Factor C in commerciallyavailable endotoxin assays. Certain proteins may also effect orcontribute to stabilization of endotoxin in undetectable soluble form.For instance, such proteins may present the endotoxin with bindingclefts offering individual endotoxin molecules a suitable environmentfor stable binding, thereby breaking up otherwise detectable endotoxinaggregates and/or preventing the endotoxin molecules from interactingwith Factor C in available endotoxin assays.

It is assumed that at least two molecules of endotoxin, that is at leasttwo molecules of LPS, must form an aggregate in order to be detectableby commercially available endotoxin tests such as the EndoLISA® test kitavailable from Hyglos GmbH and LAL-based tests.

In fact, several publications show that endotoxin aggregates aresignificantly more biologically active than disaggregated endotoxins (M.Mueller, B. Lindner, S. Kusumoto, K. Fukase, A, B. Schromm, U. Seydel,Aggregates are the biologically acitve units of endotoxin, The Journalof biological Chemistry, 2004; A. Shnyra, K. Hultenby, A. Lindberg, Roleof the physical state of Salmonella Lipopolysaccharide in expression ofbiological and endotoxic properties, Infection and Immunity, 1993).Furthermore, the activation of Factor C, described by Tan et al. (N. S.Tan, M. L. P. NG, Y. H Yau, P. K. W. Chong, B Ho, J. L. Ding, Definitionof endotoxin binding sites in horseshoe crab Factor C recombinant sushiproteins and neutralization of endotoxin by sushi peptides, The FASEBJournal, 2000), is indicated as a cooperative binding mechanism. Here,as mentioned above, at least two LPS molecules are required foractivation of Factor C, which is the key factor in limulus baseddetection methods such as the EndoLISA kit available from Hyglos GmbH.

Examples of endotoxin maskers which are detergents include anionicdetergents, cationic detergents, nonionic detergents and amphotericdetergents, and any combination thereof.

Examples of anionic detergents which may function as detergent endotoxinmaskers in the sense of the invention include alkyl sulfates such as forexample ammonium lauryl sulfate or sodium lauryl sulfate (SDS);alkyl-ether sulfates such as for example sodium laureth sulfate orsodium myreth sulfate; cholesterol sulfate; sulfonates such as forexample dodecylbenzensulfonate, sodiumlauryl sulfoacetate or xylenesulfonate; alkyl sulfo succinates such as for example disodium laurylsulfosuccinate; sulfoxides such as for example dodecyl methyl sulfoxide;phosphates such as for example trilaureth-4 phosphate; and carboxylatessuch as for example sodium stearate or sodium lauroyl sarcosinate.

Examples of cationic detergents which may function as endotoxin maskersin the sense of the invention include primary amines; secondary amines;tertiary amines; and quaternary ammonium cations such as for examplealkyltrimethylammonium salts (e.g. cetyl trimethylammonium bromide(CTAB) or cetyl trimethylammonium chloride (CTAC)); cetylpyridiniumchloride (CPC); quaternary ammonium detergents such as for exampletris[2-(2-hydroxyethoxy)ethyl]-octadecyl-ammonium phosphate (Quaternium52); and hydroxyethylcellulose ethoxylate, quaternized(Polyquaternium-10).

Nonionic detergents which may function as detergent endotoxin maskers inthe sense of the invention include polyoxyethylene glycol sorbitan alkylesters (polysorbates) such as for example polysorbate 20 (TWEEN™-20),polysorbate 40, polysorbate 60 or polysorbate 80 (TWEEN™-80);polyoxyethylene glycol alkyl ethers; polyoxypropylene glycol alkylethers; glucoside alkyl ethers; polyoxyethylene glycol octylphenolethers; polyoxyethylene glycol alkylphenol ethers; glycerol alkylesters; sorbitan alkyl esters; block copolymers of polyethylene glycoland polypropylene glycol; cocamide MEA; sterols such as for examplecholesterol; cyclodextrans; poloxamers such as for example Pluronicblock polymers (for exampleHO—(CH₂CH₂O)_(n/2)—(CH₂CH(CH₃)O)_(m)—(CH₂CH₂O)_(n/2)—H, with n=200 andm=65 for F127 and n=4.5 and m=31 for F61) and cocamide DEA.

Amphoteric detergents which may function as detergent endotoxin maskersin the sense of the invention include CHAPS(3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate); sultaines,such as for example cocamidopropyl hydroxysultaine; betaines, such asfor example cocamidopropyl betaine; amine oxides such as for examplepalmitamine oxide, laurylamine oxide and amine oxide of general formulaR³N+O⁻, wherein R³ is C₈-C₁₈ alkyl, C₈-C₁₈ alkenyl or C₈-C₁₈ alkynyl;and lecithin. Specifically, R³ in the above general formula R³N+O⁻ maybe any of C₈ alkyl, C₉ alkyl, C₁₀ alkyl, C₁₁ alkyl, C₁₂ alkyl, C₁₃alkyl, C₁₄ alkyl, C₁₅ alkyl, C₁₆ alkyl, C₁₇ alkyl or C₁₈ alkyl; or C₈alkenyl, C₉ alkenyl, Co alkenyl, C₁₁ alkenyl, C₁₂ alkenyl, C₁₃ alkenyl,C₁₄ alkenyl, C₁₅ alkenyl, C₁₆ alkenyl, C₁₇ alkenyl or C₁₈ alkenyl; or C₈alkynyl, C₉ alkynyl, C₁₀ alkynyl, C₁₁ alkynyl, C₁₂ alkynyl, C₁₃ alkynyl,C₁₄ alkynyl, C₁₅ alkynyl, C₁₆ alkynyl, C₁₇ alkynyl or C₁₈ alkynyl.

Alternatively or in addition to any of the endotoxin maskers indicatedabove (alone or in combination), the endotoxin masker may also be anactive pharmaceutical ingredient (API). This API may exist in solutiontogether with or without any of the detergent endotoxin maskersindicated above. If the API exists together with a detergent endotoxinmasker in solution, the masking effect may be more pronounced, and morestringent measures may be necessary to liberate masked endotoxin fromthe endotoxin masker, as is discussed in greater detail below. APIswhich may especially engender or augment the masking of endotoxinpresent in the solution are protein APIs, for example an antibody; anantibody fragment; a hormone; an enzyme; a fusion protein; a proteinconjugate; and any combination thereof. When the protein API is anantibody fragment, the antibody fragment may be preferably chosen fromthe group consisting of: Fab; a Fab′; a F(ab′)2; an Fv; a single chainantibody; and any combination thereof. When the protein API is anantibody, the antibody may be preferably chosen from the groupconsisting of: a fully human antibody; an anti-idiotype antibody; ahumanized antibody; a bispecific antibody; a chimeric antibody; aCDR-grafted antibody; a monoclonal antibody; a polyclonal antibody; andany combination thereof. Alternatively or in addition to the above, theAPI may also be a small organic molecule. The skilled person understandswhat is meant by the term “small organic molecule” or “small molecule”.This is a molecule with a molecular weight of no more than 300 g/mol,400 g/mol, 500 g/mol, 600 g/mol, 700 g/mol, 800 g/mol, 900 g/mol or,preferably, 1000 g/mol.

Generally, an endotoxin masker, whether a detergent or a protein, willhave the characteristic of shifting the equilibrium between solubilizedand aggregated endotoxin in the direction of solubilized endotoxin whichis not detectable by available endotoxin assays. It is this shifting ofendotoxin into an undetectable form which is referred to as “masking”herein. As mentioned above, the form in which the endotoxin issolubilized may for example include endotoxin a) being embedded in thelipid layer of a micelle formed by a detergent; b) being bound on or ina protein, e.g. in a suitable binding cleft of appropriate steric andelectrostatic environment formed on the surface of an activepharmaceutical agent, e.g. a protein; or c) participating in acombination of these two possibilities. Regardless of the form in whichendotoxin is solubilized so as to energetically disfavor the aggregateform, however, the net effect is that individual molecules of endotoxinwhich would otherwise be aggregated and therefore detectable, areindividually stabilized and, in this individualized (solubilized) form,become and remain undetectable, i.e. masked.

Although undetectable, however, such stabilized endotoxin molecules insolution can nevertheless engender and/or contribute to the sorts ofpyrogenic and/or toxic reactions outlined above when administered tosubjects. This danger is especially acute in pharmaceuticalformulations, since pharmaceutical formulations often contain adetergent to solubilize an API, e.g. a protein API, which, without thedetergent, would be insoluble at the concentrations provided in thepharmaceutical formulation. In rendering the API, e.g. protein API,soluble by including detergent, then, one often unwittingly destroys thevery aggregation of endotoxin which is needed for detection of thisendotoxin. Thus, when the endotoxin masker is a detergent, the verymeasure employed to formulate the API, e.g. protein API, in acceptableform and concentration also has the potential to mask endotoxin insolution.

As mentioned above the endotoxin masker may also be a protein, forinstance the API itself. This scenario may arise in conjunction with thepresence of a detergent endotoxin masker or, in the event that nodetergent is present, may also arise in the absence of a detergentendotoxin masker. In this latter case, the API, in particular a proteinAPI, may offer the endotoxin a sufficient environment for stable bindingon or in such protein such that the endotoxin is masked by the APIalone, i.e. without any detergent being necessary to mask endotoxin,rendering it undetectable. In the event that the endotoxin masker is aprotein, this protein may be the API itself, or may alternatively oradditionally be a protein in solution which is different from the API.Generally, any protein having an appropriate steric and electrostaticenvironment to stabilize individual molecules of endotoxin, for instanceindividual molecules of LPS could potentially effect or contribute tothe masking of endotoxin.

It is a hallmark of the invention that when the endotoxin masker is aprotein, either alone or together with an additional endotoxin maskersuch as e.g. a detergent endotoxin masker, unmasking the endotoxinleaves the protein endotoxin masker chemically unaltered followingunmasking. In particular, unmasking the endotoxin does not cleave orotherwise degrade the protein endotoxin masker (e.g. protein API).

In scenarios of the type described above, individual molecules ofendotoxin which would otherwise remain in aggregates and thereforedetectable, are stabilized at one or more such surface locations on orin said protein. As is the case for detergent micelles, suchstabilization shifts the equilibrium existing between solubilized(undetectable) and aggregated (detectable) in the direction ofsolubilized (undetectable) endotoxin. As mentioned above, one mayimagine such a shift of equilibrium toward the solubilized(undetectable) form as being especially pronounced in the event that asolution comprises both detergent and one or more proteins with theabove characteristics, since in such cases the stabilization ofindividual molecules of endotoxin out of its aggregate form by theendotoxin masker may ensue both in the form of stabilization in micellesas well as on the surface of proteins. In such scenarios, more stringentmeasures may be required to shift said equilibrium toward the aggregateendotoxin form which is then detectable. These are discussed in moredetail in the context of illustrative scenarios further below (FIGS.1-6).

Modulator

The term “modulator” as used herein refers to one or more compoundswhich, alone or in concert, render(s) a masked endotoxin susceptible todetection by an endotoxin assay (such as the EndoLISA® detection assayavailable from Hyglos GmbH). The term “modulator” as used herein mayencompass both single as well as multiple components which achieve thisend. In some instances herein below, reference is made to a “modulatorsystem”, although the term “modulator” is sometimes used to designatemultiple modulator substances which are intended to work in concert.This refers to a multi-component modulator comprising multiplesubstances which act in concert to render a masked endotoxin detectableby an endotoxin assay. The different components of a modulator systemmay be incorporated for different reasons, i.e. to take advantage ofdifferent functions of modulator substances which affect the stabilityof a complex between endotoxin and endotoxin masker in different ways.For ease of reference, one may for example refer to different kinds ofmodulator which may be employed alone or together to unmask endotoxin:

-   -   “Disrupting modulator”: A “disrupting modulator” is a modulator        which completely or partially breaks up a complex between an        endotoxin masker and an endotoxin. When the endotoxin masker is        a detergent, and the endotoxin is masked in solubilized form        inserted in the lipid layer of a masking detergent micelle, then        a modulator which disrupts such a detergent micelle so as to        liberate the endotoxin would be referred to as a disrupting        modulator. As discussed in greater detail below, 1-dodecanol is        one such disrupting modulator. A disrupting modulator, for        example 1-dodecanol, 1-decanoic acid or sodium octyl sulfate        (SOS) may advantageously be used in a concentration range of        0.01-100 mM, preferably in a concentration range of 0.1-10 mM,        preferably at a concentration of 10 mM in the unmasking process.        In some cases, the disrupting modulator may also simultaneously        function as a reconfiguring modulator, described below.    -   “Adsorbing modulator”: An “adsorbing modulator” is a modulator        which has the ability to bind substances which would otherwise        stabilize the endotoxin in solubilized and therefore        non-detectable form. For instance, when the endotoxin masker is        a detergent as e.g. contained in some pharmaceutical        compositions, then a modulator which binds molecules of the        detergent and in this way contributes to the breakdown of        endotoxin-stabilizing micelles would be referred to as an        adsorbing modulator. As discussed in greater detail below, BSA        is one such adsorbing modulator. An adsorbing modulator, for        example BSA may advantageously be used in a concentration range        of 0.1-20 mg/mL, preferably in a concentration range of 1-10        mg/mL, preferably at a concentration of 10 mg/ml in the        unmasking process.    -   “Displacing modulator”: A “displacing modulator” is a modulator        which has the ability to completely or partially displace a        molecule of endotoxin from its stable binding position in or on        an endotoxin masker. For instance, when the endotoxin masker is        a protein, and the endotoxin is bound in or on a protein which        stabilizes the endotoxin in undetectable form, then a modulator        which has the ability to replace the endotoxin in or on the        protein, e.g. by means of hydrophobic interactions, would be        referred to as a displacing modulator. As discussed in greater        detail below, SDS is one such displacing modulator. A displacing        modulator, for example SDS, may advantageously be used in a        concentration range of 0.01-1%, preferably in a concentration        range of 0.05-0.5%, preferably at a concentration of 0.1% in the        unmasking process.    -   “Reconfiguring modulator”: A “reconfiguring modulator” is a        modulator which has the ability to transiently stabilize        endotoxin following its liberation from the endotoxin masker        (e.g. by a disrupting modulator or displacing modulator, as        discussed above), thus helping the liberated, solubilized        (undetectable) endotoxin to adopt an aggregated (detectable)        form. With the help of the reconfiguring modulator, solubilized        endotoxin becomes reconfigured as aggregated endotoxin. As        discussed in greater detail below, 1-dodecanol is one such        reconfiguring modulator. A reconfiguring modulator, for example        1-dodecanol, 1-decanoic acid or sodium octyl sulfate (SOS) may        advantageously be used in a concentration range of 0.01-100 mM,        preferably in a concentration range of 0.1-10 mM in the        unmasking process. In some cases, the reconfiguring modulator        may also simultaneously function as a disrupting modulator,        described above.

As will become clear herein below, the above types of modulator are notmutually exclusive; that is, it is possible for a given substance tohave functionality as different kinds of modulators above. One exampleis 1-dodecanol, which may be classified as both a disrupting modulator(breaking up a detergent micelle) as well as a reconfiguring modulator(transiently stabilizing the micelle-liberated endotoxin so it canaggregate and become detectable). Similarly SDS may be classified as adisrupting modulator (breaking up existing micelles of another, non-SDSdetergent) and a displacing modulator (liberating endotoxin from bindingsites in or on any masking protein which may be present). Theclassification as to the type of modulator depends on the function thata substance in question plays in a particular composition. However,since it is assumed that reconfiguring of the endotoxin from solubilizedinto aggregated form will generally be required in order to render theendotoxin detectable, the modulator will normally comprise at least onecomponent qualifying as a “reconfiguring modulator”.

As a further example, a substance which functions as a “displacingmodulator” when the endotoxin masker is a protein may in some casesfunction as a “disrupting modulator” when the endotoxin masker is adetergent. SDS is one example of such a substance, the classification ofwhich as to the type of modulator component depends on the prevailingconditions. For instance, when the endotoxin masker is a protein, SDSwill generally function as a displacing modulator, since it helps todisplace the endotoxin bound in or on the masking protein. However, whenthe endotoxin masker is a detergent, then SDS, alone or together withanother modulator component, may function more as a disruptingmodulator, since in this case it promotes the liberation of endotoxinfrom the lipid layer of detergent micelles by disrupting the micelles.

A modulator may contain one or more substances within the aboveclassifications. For instance, a single component modulator may compriseonly a disrupting modulator such as 1-dodecanol. A dual-componentmodulator may comprise a mixture of a disrupting modulator such as1-dodecanol (also possibly functioning as a reconfiguring modulator)and, depending on the nature of the masking complex between endotoxinand endotoxin masker, one of an adsorbing modulator such as BSA or adisplacing modulator such as SDS. A multi-component modulator maycomprise a mixture of a disrupting modulator such as 1-dodecanol (alsopossibly functioning as a reconfiguring modulator) and, depending on thenature of the masking complex between endotoxin and endotoxin masker,one each of an adsorbing modulator such as BSA and a displacingmodulator such as SDS. As will be discussed in detail below, thecomplexity of the modulator system chosen will depend on the nature ofthe complex between endotoxin and endotoxin masker, and the surroundingsolution conditions which contribute to the stability of that complex.From the above, it is clear that each new composition to be analyzed forthe presence of endotoxin may require its own customized modulatorcomposition in order to render the masked endotoxin susceptible todetection. The identification of a suitable modulator for a givencomposition or formulation to be tested can however be accomplished byroutine experimentation, as will be shown further below.

As mentioned above, in its most general sense, the modulator is assumedto destabilize a complex between endotoxin and an endotoxin masker andto promote the liberation of the endotoxin from the endotoxin masker. Inthis way, the modulator or modulator system effectively shifts theequilibrium from a solubilized (undetectable) state toward an aggregated(detectable) state.

The present inventors have surprisingly found that endotoxin which ispresent but undetectable in solution remains undetectable because, asassumed, the endotoxin remains stably solubilized in detergent micellesand/or bound to surface structures of proteins present in the solution.Individually stabilized in this form, the endotoxin molecules evadedetection. However, the present inventors have found that solutionconditions can be manipulated such that solubilized endotoxin isrendered into a form which can be detected. In some instances, multiplemanipulations of solution conditions may be required to reach this endand the stringency of the measure or measures taken to effect thedesired shift in equilibrium toward an aggregated state will varydepending on the degree to which the endotoxin masker stabilizes theendotoxin in solubilized form, as mentioned above. But generally, themanipulations performed in accordance with the invention as describedherein should be understood in the context of the overall aim ofshifting the equilibrium of endotoxin from a solubilized state to anaggregated state such that it can be detected.

In order to accomplish the above, the “modulator” will generally includean amphiphilic molecule which competes for binding between the lipidcomponent of endotoxin and the endotoxin masker, thus weakening theinteraction between the former and the latter. Such competitive bindingwill generally be accomplished by providing at least one component ofthe modulator system in a form which is structurally similar to the(amphiphilic) lipid component of the endotoxin such that the former maydisplace the latter in its stabilized interaction with the endotoxinmasker.

For instance, in the event the endotoxin masker is a detergent, asuitable disrupting modulator will generally include an amphiphiliccompound capable of stably inserting i.e. between the amphiphilicdetergent molecules and the similarly amphiphilic lipid portion of theendotoxin. When the endotoxin masker is a detergent, an amphiphilicdisrupting modulator will therefore elicit several effects in parallelwhich are conducive to an overall shift in equilibrium from asolubilized toward an aggregated form of endotoxin. First, providing amodulator system comprising at least one amphiphilic disruptingmodulator disrupts the lipophilic interactions underlying the detergentmicelles such that these micelles are broken up. Since endotoxin waspreviously solubilized (and therefore masked) by insertion of its lipidcomponent into the lipid layer of the detergent micelles, the breakup ofthe micelles removes this stabilizing force and results in theliberation of previously embedded endotoxin. The role of the disruptingmodulator in the event that the endotoxin masker is or includes adetergent is thus to break up detergent micelles.

Further, the amphiphilic character of the disrupting modulator may alsoenable it to associate with the lipid component of the endotoxin, oncethe endotoxin is liberated from its detergent micelles as describedabove. This interaction between the amphiphilic disrupting modulator andthe lipid component of the endotoxin has the effect of chaperoning theendotoxin in aqueous solution following its liberation from thestabilizing detergent micelles. In this event, the disrupting modulatorwould have a double function as a reconfiguring modulator. When thedisrupting modulator is amphiphilic in character, it is not excludedthat it may be capable for forming micelles of its own. However, theunmasking effect will generally be greatest when the amphiphilicdisrupting modulator does not form micelles of its own which mightsimply swap one solubilized and therefore masked endotoxin state foranother. A key role of the reconfiguring modulator is thus totransiently stabilize liberated endotoxin (albeit less than in itsprevious complex with the endotoxin masker), effectively chaperoning theendotoxin into an aggregated and therefore detectable state.

Thus temporarily chaperoned in solution, the liberated endotoxin is thenfree to aggregate into a form which is detectable and therefore“unmasked”. Whether or not further manipulation of solution conditionsbeyond addition of the modulator or modulator system is necessary toshift equilibrium towards this aggregated, detectable form willgenerally depend on the conditions prevailing in solution and theinitial stability of the endotoxin as complexed with the endotoxinmasker.

In another scenario already contemplated above, the endotoxin masker isnot, or not only a detergent, but may also be or comprise a protein withbinding clefts on its surface suitable to stably bind individualmoieties of endotoxin such that it cannot be detected. In this event,similar considerations pertaining to the modulator apply as set outabove. For instance, use of a disrupting (amphiphilic) modulator and/ora displacing modulator in the event that the endotoxin is or comprises aprotein has the effect that the modulator disrupts the lipophilicinteractions existing between lipophilic amino acid side chains of theprotein (endotoxin masker) and the lipid component of the endotoxin.Because the disrupting modulator and/or displacing modulator is/arelikely to be amphiphilic in character, the modulator(s) would also beable to disrupt electrostatic interactions existing between polar and/orionized side chains within the protein (endotoxin masker) and polargroups within the core and/or O-antigen polysaccharide regions of theendotoxin. With these stabilizing interactions disrupted, the endotoxinwhich was previously masked by a protein endotoxin masker is thusdisplaced from its previous complex with the protein, and is chaperonedin solution into an aggregated state by association with areconfiguration modulator as described above.

As described above for the case in which the endotoxin masker is adetergent in the absence of a protein endotoxin masker, the liberatedand reconfiguation modulator-chaperoned endotoxin is then free toaggregate into a form which is detectable and therefore “unmasked”.Whether or not further manipulation of solution conditions beyondaddition of the components of the modulator system is necessary to shiftequilibrium towards this aggregated, detectable endotoxin form willgenerally depend on the conditions prevailing in solution and theinitial stability of the endotoxin as complexed with the endotoxinmasker.

The modulator, e.g. the disrupting modulator, the displacing modulatorand/or the reconfiguring modulator may in certain embodiments comprise afirst heteroatom-substituted aliphatic, wherein the main chain of thefirst heteroatom-substituted aliphatic comprises 8 to 16 carbon atoms.As used herein, the term “main chain” refers to the longest chain of thefirst heteroatom-substituted aliphatic comprising 8 to 16 carbon atoms,as numbered by standard IUPAC nomenclature. Specifically, the main chainof the first heteroatom-substituted aliphatic may comprise 8, 9, 10, 11,12, 13, 14, 15 or 16 carbon atoms. As used herein, the term “heteroatom”refers to any atom other than carbon, to which a carbon atom in thefirst heteroatom-substituted aliphatic is covalently bound.Representative heteroatoms include oxygen, nitrogen and sulfur atoms. Ina further preferred embodiment, the oxygen-substituted aliphatic is analiphatic alcohol, in particular, 1-dodecanol, that is the moleculegiven by the formula HO—(CH₂)₁₁—CH₃. As mentioned above, 1-dodecanol isespecially well suited in many instances as a disrupting modulator aswell as, in most if not all instances, as a reconfiguring modulator.

The reconfiguring modulator is assumed to play an especially important,if not indispensible role in promoting an aggregated, detectable form ofendotoxin. The reconfiguring modulator may be a heteroatom-substitutedaliphatic comprising 8, 9, 10, 11, 12, 13, 14, 15 or 16 carbon atoms inits main chain. The term “main chain” refers to the longest chain of thereconfiguring modulator, as numbered by standard IUPAC nomenclature. Asused herein, the term “heteroatom” refers to any atom other than carbon,to which a carbon atom in the first heteroatom-substituted aliphatic iscovalently bound. Representative heteroatoms include oxygen, nitrogenand sulfur atoms. It is especially suitable when the heteroatom isoxygen. Furthermore, the reconfiguring modulator may be branched orunbranched, with the branched variants comprising substitutions alongthe “main chain” as defined above. Said substitutions may be e.g.methyl, ethyl, propyl and/or butyl. An unbranched chain is preferred.The reconfiguring modulator may be saturated to various extents, and mayfor example comprise a C₈ alkyl, C₉ alkyl, C₁₀ alkyl, C₁₁ alkyl, C₁₂alkyl, C₁₃ alkyl, C₁₄ alkyl, C₁₅ alkyl or C₁₆ alkyl moiety; or a C₈alkenyl, C₉ alkenyl, C₁₀ alkenyl, C₁₁ alkenyl, C₁₂ alkenyl, C₁₃ alkenyl,C₁₄ alkenyl, C₁₅ alkenyl or C₁₆ alkenyl moiety; or a C₈ alkynyl, C₉alkynyl, C₁₀ alkynyl, C₁₁ alkynyl, C₁₂ alkynyl, C₁₃ alkynyl, C₁₄alkynyl, C₁₅ alkynyl or C₁₆ alkynyl moiety. Furthermore, thereconfiguring modulator may contain any mixture of single, double andtriple carbon-carbon bonds. Especially suitable reconfiguring modulatorsare saturated, i.e. comprise C₈ alkyl, C₉ alkyl, C₁₀ alkyl, C₁₁ alkyl,C₁₂ alkyl, C₁₃ alkyl, C₁₄ alkyl, C₁₅ alkyl or C₁₆ alkyl. Especiallysuitable reconfiguring modulators comprise C₁₂ alkyl. Furthermore, theheteroatom may be of various oxidation states. For instance, when theheteroatom is oxygen, the oxygen may be in the form of an alcohol, analdehyde or a carboxylic acid.

Especially suitable as reconfiguring modulators are molecules inunbranched alkanols, in particular unbranched 1-alkanols. Among these,especially suitable are C₁₂ alkanols, especially 1-dodecanol having theformula HO—(CH₂)₁₁—CH₃.

In further embodiments, the modulator system may include othercomponents in addition to said first heteroatom-substituted aliphaticcomprising 8 to 16 carbon atoms. For example, the modulator system mayadditionally comprise a second heteroatom-substituted aliphatic, e.g. asa disrupting modulator, a displacing modulator and/or a reconfiguringmodulator, wherein the main chain of said second heteroatom-substitutedaliphatic comprises 8 to 16 carbon atoms. The “main chain” of the secondheteroatom-substituted aliphatic is defined as described above for thefirst heteroatom-substituted aliphatic. Specifically, the main chain ofthe second heteroatom-substituted aliphatic may comprise 8, 9, 10, 11,12, 13, 14, 15 or 16 carbon atoms. The first heteroatom-substitutedaliphatic comprising 8 to 16 carbon atoms is different than the secondheteroatom-substituted aliphatic comprising 8 to 16 carbon atoms. In apreferred embodiment, the second heteroatom-substituted aliphatic whichmay be part of the modulator is an oxygen-substituted aliphatic. Incertain preferred embodiments, this oxygen-substituted aliphatic is analiphatic sulfate, wherein it is especially preferred that thisaliphatic sulfate is sodium dodecyl sulfate (SDS). Thus, in aparticularly preferred embodiment of the invention, the modulator systemincludes a first heteroatom-substituted aliphatic which is 1-dodecanol(e.g. as a disrupting modulator and/or a reconfiguring modulator), and asecond heteroatom-substituted aliphatic which is SDS (as a furtherdisrupting modulator and/or a displacing modulator).

In a further embodiment, the modulator system as described above mayfurther comprise a protein capable of binding a detergent so as to breakup micelles formed by said detergent. Generally, the detergent boundwill be the endotoxin masker (when said endotoxin masker is or comprisesa detergent), and the principle by which the protein capable of bindinga detergent binds the detergent is analogous to the principle describedabove, according to which a protein which functions as an endotoxinmasker sequesters portions of the endotoxin molecule in or on itssurface. In the present embodiment, the protein capable of binding adetergent, when used as part of the modulator, also bears on its surfaceareas of steric and electrostatic compatibility with a portion orportions of detergent molecules present in solution, which aresufficient to bind or sequester detergent molecules, thus rendering themunavailable for participation in micelles and thus breaking up anydetergent micelles which may be harbor endotoxin, or which may serve toshift equilibrium away from an aggregated form of endotoxin.

The inventors have found that albumin molecules are exceptionally goodat binding detergent. Thus, it is contemplated that in addition to thefirst heteroatom-substituted aliphatic alone, or in addition to thefirst heteroatom-substituted aliphatic in combination with the secondheteroatom-substituted aliphatic, the modulator may additionallycomprise a protein (adsorbing modulator) capable of binding a detergentso as to break up micelles formed by said detergent. In certainembodiments, the protein component of the modulator may be an albumin,preferably human serum albumin (HSA), bovine serum albumin (BSA) orovalbumin (OVA).

It is additionally contemplated that the modulator may contain one ormore of each of the first heteroatom-substituted aliphatic comprising 8to 16 carbon atoms, the said second heteroatom-substituted aliphaticcomprising 8 to 16 carbon atoms and said protein capable of binding adetergent so as to break up micelles formed by said detergent. In apreferred embodiment of the invention, the modulator comprises1-dodecanol alone. In a further preferred embodiment of the invention,the modulator comprises 1-dodecanol and SDS. In a further preferredembodiment of the invention, the modulator comprises 1-dodecanol, SDSand HSA. In a further preferred embodiment of the invention, themodulator comprises 1-dodecanol, SDS and BSA.

Composition

As used herein, the term “composition” refers to a mixture comprising(at least) an endotoxin masker. The endotoxin, even if present andmasked, remains undetectable in the composition. The composition ispreferably a pharmaceutical composition, e.g. a composition comprisingan active pharmaceutical ingredient, or API. The term “composition” maybe e.g. an extract; vaccine; any composition suitable for parenteraladministration, i.e. parentalia; any composition suitable forintraperitoneal, transdermal, subcutaneous or topical administration; ablood product; a cell therapy solution, e.g. intact, living cells, forexample, T cells capable of fighting cancer cells; a gene therapysolution, e.g. a solution capable of nucleic acid polymer delivery intoa patient's cells as a drug to treat disease; an implant or medicaldevice; or a composition resulting from rinsing or wiping the surface ofan object, said object for instance being a medical device, an implantor a filling machine.

Detection Method

As used herein, the term “detection method” refers to a method which issuitable for detecting endotoxin in solution. For example, suitablemethods in this regard are limulus based detection methods, or is anenzyme linked immunosorbent assays (ELISA). The limulus methods can beperformed classically by using natural derived lysate (J. Jorgensen, R.Smith, Perparation, Sensitivity, and Specificity of Limulus Lysate forEndotoxin Assay, Applied Microbiology, 1973) or recombinantly preparedFactor C (J. L. Ding, B. Ho, A new era in pyrogen testing, Trends inBiotechnology, 2001). The most promising of such methods areenzyme-linked affinitysorbent assays, using a solid phase for endotoxincapturing and subsequent detection by recombinant version of a proteinin the LAL assay, Factor C. The EndoLISA® kit is one suchaffinitysorbent assay (H. Grallert, S. Leopoldseder, M. Schuett, P.Kurze, B. Buchberger, EndoLISA®: a novel and reliable method forendotoxin detection, Nature Methods, 2011). The EndoLISA® detectionsystem is for example described in the book “PharmazeutischeMikrobiologie—Qualitatssicherung, Monitoring, Betriebshygiene” byMichael Rieth, October 2012, Wiley-VCH, Weinheim, ISBN978-3-527-33087-4.

Agent which Influences Hydrogen Bonding Stability in Solution

According to a further embodiment of the invention, the above methods ofunmasking an endotoxin and/or the method of detecting an endotoxin mayfurther comprise the step of adding to said composition an agent whichinfluences hydrogen bonding stability in solution. Generally, as usedherein, an agent which influences hydrogen bonding stability in solutionmodifies solution conditions so as to destabilize the complex in whichan individual molecule or multiple molecules of endotoxin is/aresolubilized and therefore masked.

Not all complexes between endotoxin and endotoxin masker are the same.In particular, the energy minima governing endotoxin stabilization incertain masking complexes are different than those governing endotoxinstabilization in other masking complexes. All other things being equal,the lower an energy minimum governing the stabilization of endotoxin ina given complex with an endotoxin masker is, the more difficult it willbe, i.e. the more stringent the modulator must be, to liberate endotoxinfrom its solubilized state. Yet as mentioned above, such liberation isan important step in the eventual aggregation of endotoxin into adetectable, i.e. unmasked, form. Thus, the more stable the complexbetween endotoxin and endotoxin masker, the more rigorous must be themeasures taken to ultimately unmask the endotoxin.

In instances where the complex between endotoxin and endotoxin masker isespecially stable, addition of a single- or even multiple-componentmodulator may sometimes not be enough to destabilize the masking complexand liberate the endotoxin. It may in such instances be helpful topromote endotoxin liberation from its complex with endotoxin masker byadjusting solution conditions so as to destabilize theendotoxin-endotoxin masker complex.

As mentioned above, an agent which influences hydrogen bonding stabilityin solution may assist in this aim. Some, if not most of thestabilization of endotoxin in complex with an endotoxin masker normallyarises from non-covalent interactions between the endotoxin moiety andthe endotoxin masker. These interactions may for instance take the formof hydrophobic, ionic, hydrogen bonding and/or Van der Waalsinteractions between regions of the endotoxin molecule and regions onthe molecule or molecules of the endotoxin masker. As the strength ofthese endotoxin-endotoxin masker interactions is influenced by thesurrounding hydrogen bonding network in solution, it conversely followsthat influencing the hydrogen bonding stability in solution willmodulate the strength of these interactions.

Addition of an agent which influences hydrogen bonding stability insolution can therefore help to weaken the noncovalent bondinginteractions between endotoxin and endotoxin masker, essentially raisingthe free energy of the complex and thus rendering it more susceptible todisruption by the modulator so that the endotoxin is liberated andrendered detectable.

Besides the destabilizing effect discussed above, an agent whichinfluences hydrogen bonding stability in solution may also have afurther effect promoting endotoxin unmasking. By altering hydrogenbonding stability in solution, the agent may also foster aggregation ofthe endotoxin moieties once liberated from their complex with endotoxinmasker. There will generally exist an equilibrium between endotoxin insolubilized and aggregated forms. The agent which influences hydrogenbonding stability in solution can be helpful in shifting thisequilibrium towards the aggregated (and thus detectable). Suitablesubstances are those which would tend to decrease the hydrogen bondingstability in solution surrounding the chaperoned endotoxin moities,and/or compounds which tend to increase the ionic strength of thesolution, thus driving the reconfiguring modulator-chaperoned endotoxinmoieties together into a lipophilic aggregate.

It should be noted that it may not always be necessary to add an agentwhich influences hydrogen bonding stability in solution. Whether or notaddition of such an agent will be indicated will depend, for instance,on the stability of endotoxin in complex with the endotoxin maskerand/or on the position of equilibrium between solubilized, chaperonedand aggregated forms of endotoxin moieties once liberated from theendotoxin masker. For instance, in solutions containing higherconcentrations of salt, it is conceivable that the complex of theendotoxin and endotoxin masker may already be instable enough to bebroken up by the disrupting modulator alone, and that the endotoxinmoieties present in solution following liberation from the endotoxinmasker will be instable enough so as to form aggregates without anyfurther assistance. In such situations, an agent which influenceshydrogen bonding stability in solution may not be required to achieveunmasking.

On the other hand, there may exist situations, for instance in solutionscontaining lower concentrations of salt, where the endotoxin-endotoxinmasker complex may be of such great stability that a disruptingmodulator alone cannot break it up to liberate endotoxin, or where—evenif liberated by disrupting modulator alone—the equilibrium betweensolubilized and aggregated endotoxin lies towards the solubilized formso that the aggregation needed for detection does not occur. In suchsituations incorporation of an agent which influences hydrogen bondingstability in solution may help to influence the energetics ofcomplexation and/or aggregation so as to favor endotoxin in detectableform.

In general, it can be said that the degree of destabilization of thecomplex between the endotoxin and endotoxin masker will depend on theamount of salt in solution, with this complex being destabilized to anextent directly proportional to the amount of salt present in solution.As a general rule though, reference may be made to the Hofmeisterseries, according to which the more chaotropic a salt is, the lower theamount of such a salt will be needed to destabilize a complex betweenendotoxin and endotoxin masker to a given extent. Merely as anillustrative example, in order to achieve approximately the same degreeof destabilization of a complex between endotoxin and endotoxin maskerachievable with, say, 100 mM CaCl₂, one may need to use, say, 500 mMNaCl. In this example, CaCl₂ is more chaotropic than NaCl, so less CaCl₂would be required to achieve the same degree of destabilization.

In certain embodiments of the invention, the agent which influenceshydrogen bonding stability in solution may be a chaotropic agent, acation or a combination thereof. In certain embodiments, the chaotropicagent may be chosen from the group consisting of urea, guanidiniumchloride, butanol, ethanol, lithium perchlorate, lithium acetate,magnesium chloride, phenol, a propanol (e.g. 1-propanol or 2-propanol,i.e. isopropanol) and thiourea. In certain embodiments, the cation is adivalent cation, for example Ca²⁺, Mg²⁺, Sr²⁺ and/or Zn²⁺. An expeciallypreferred divalent cation is Ca²⁺.

The agent which influences hydrogen bonding stability in solution, e.g.CaCl₂, may advantageously be used in a concentration range of 1-400 mM,preferably in a concentration range of 10-200 mM, preferably at aconcentration range of 50-100 mM in the unmasking process.

Without being bound by theory, and merely to illustrate the principlesand possible mechanisms which the present inventors believe underlie theobserved advantageous effect of unmasking endotoxin in solution, therebyrendering previously masked an undetectable endotoxin detectable, thefollowing describes several mechanisms of interaction between endotoxinand further components of a given composition containing at least oneendotoxin masker. To illustrate these mechanisms, reference is made toFIGS. 1-6.

Unmasking Endotoxin Masked by a Detergent Masker with a Single-ComponentModulator, in which the Single Component Functions as Both a DisruptingModulator and a Reconfiguring Modulator

FIG. 1 depicts the scenario in which endotoxin resides in solutiontogether with a detergent which is masking it in individualized form ina detergent micelle. Panel (a) of FIG. 1 shows a single endotoxin moietywhich is inserted in the lipid layer of such a detergent micelle via itslipid tail. The detergent molecules constituting the lipid layer of thedetergent micelle are symbolized as open circles in panel (a). Becausethis single moiety of endotoxin is stably inserted in individual form inthe lipid layer of the micelle rather than in multimeric, aggregatedform, it evades detection using available detection methods (e.g. theEndoLISA® assay of Hyglos GmbH). If the solution shown in panel (a) ofFIG. 1 were a pharmaceutical formulation additionally containing an API,it would appear to be endotoxin-free and therefore safe foradministration, even though endotoxin is present in the solution.Administering such an ostensibly endotoxin-free formulation to a patientwould thus risk unwittingly eliciting the types of dangerousimmunological and toxic responses to endotoxin mentioned above.

Above the equilibrium arrows between panels (a) and (b) of FIG. 1, onesees the addition of a disrupting and reconfiguring modulator capable ofreleasing the endotoxin from a complex between the endotoxin and theendotoxin masker. In the scenario shown in in FIG. 1, this “complex” isthe endotoxin embedded, via its lipid component, in the lipid layer of adetergent micelle. The disrupting and reconfiguring modulator shown here(an amphiphilic molecule used as a single-component modulator havingcapacity as both a disrupting and reconfiguring modulator) exhibits thedual properties of breaking up the detergent micelle so as to liberateinserted molecules of endotoxin, as well as of stabilizing the endotoxinonce it is liberated from its complex with the endotoxin masker. Thislatter characteristic is schematically depicted in the upper portion ofpanel (b) of FIG. 1, showing a molecule of endotoxin stabilized by thedisrupting and reconfiguring modulator such that the molecule ofendotoxin can exist in chaperoned form outside of the micelles oncethese are broken up by the modulator. The lower portion of panel (b)makes clear that the disrupting modulator exists in equilibrium,associated with both the liberated endotoxin moiety and detergentpreviously making up the lipid layer of the detergent micelle prior tothe micelles disruption by the disrupting (and reconfiguring) modulator.

As mentioned above, in one embodiment of the present invention, thedisrupting and/or reconfiguring modulator may be 1-dodecanol, bearing apolar alcohol moiety, followed by a saturated hydrocarbon tail of 12carbon atoms. Both the steric and electrostatic configuration of1-dodecanol is thus similar to that of the lipid moieties of theendotoxin, so that 1-dodecanol can efficiently interact with, andtherefore stabilize, the endotoxin after it has been liberated from thedetergent micelle.

Another reason why 1-dodecanol is especially suitable for use as adisrupting and/or reconfiguring modulator is that 1-dodecanol, althoughamphiphilic, does not form micelles. Thus, once the detergent micelledepicted in panel (a) of FIG. 1 is broken up by 1-dodecanol, newmicelles of modulator do not reform, which might otherwise remaskendotoxin by shifting equilibrium away from its aggregated form. Thecharacteristic of the modulator that it does not form micelles itselfthus contributes to the stabilization of endotoxin in solution, aided bythe modulator, as depicted in panel (b) of FIG. 1. In the scenariodepicted in FIG. 1, the hypothetical prevailing solution conditions aresuch that equilibrium between the chaperoned moieties of endotoxin shownin panel (b) and the aggregated endotoxin shown in panel (c) alreadylies in the direction of the aggregate of panel (c). With the aggregateform of endotoxin favored, the endotoxin is already in, or predominantlyin an aggregated form which is amenable to detection by known means,e.g. the EndoLISA® test kit of Hyglos GmbH.

Overall, then, FIG. 1 shows the transition from individual endotoxinmoieties (solubilized) which are stably inserted in and therefore maskedby detergent micelles to a scenario in which the individual moieties ofendotoxin have aggregated so as to become detectable. Previously maskedendotoxin in panel (a) has been unmasked in panel (c), thereby allowingone to determine that a solution previously thought to be free ofendotoxin actually contains this contaminant.

Unmasking Endotoxin Masked by a Detergent Masker with a Dual-ComponentModulator Comprising a Disrupting and Reconfiguring Modulator and anAdsorbing Modulator (Protein)

The initial scenario depicted in FIG. 2 is much like that depicted inFIG. 1: a single molecule of endotoxin is inserted in a detergentmicelle (symbolized by a ring of open circles representing theindividual detergent molecules) and, thus stably individualized, ismasked such that it evades detection. Between panels (a) and (b), onesees the addition of a dual-component modulator system comprising both anon-protein component functioning simultaneously as a disrupting andreconfiguring modulator and a protein component functioning as anadsorbing modulator. The disrupting and reconfiguring modulator may beas described as above for FIG. 1, e.g. 1-dodecanol, which helps todisrupt the detergent micelle and stabilize/reconfigure the liberatedendotoxin, without forming micelles of its own. The adsorbing modulatormay for example be added as part of the modulator in order to promotethe disruption of detergent micelles which are more stable than thosedepicted in FIG. 1, and for which a disruption modulator alone may notsuffice to achieve the desired disruption.

As explained above, the adsorbing modulator may for instance be bovineserum albumin (BSA) or human serum albumin (HSA), among other things.Such proteins have the ability to act as “molecular sponges” whichadsorb on their surface molecules of the previously micelle-formingdetergent. Of course, in the event that such an adsorbing modulator isemployed, there will exist a certain equilibrium between otherdetergent-like molecules in solution, such as the disrupting andreconfiguring modulator. This would be expected to engender anequilibrium as shown in panel (b), in which the disrupting andreconfiguring modulator exists in forms bound to liberated endotoxin(right portion of panel (b)), bound to detergent previously constitutingthe detergent micelle, as well as bound to the surface of the adsorbingmodulator, along with additional detergent from the (now disrupted)detergent micelle.

Under the solution conditions prevailing in the scenario shown in FIG.2, endotoxin which has been liberated from the masking detergent micellecombine into detectable aggregates, shown in panel (c). In fact, the useof an adsorbing modulator as shown in FIG. 2 can promote such aggregateformation. This is assumed to be because the adsorbing modulator bindsmolecules of the disrupting and reconfiguring modulator on its surface,thereby removing these otherwise endotoxin-stabilizing species fromsolution such that equilibrium is driven to the right toward theaggregate of panel (c).

Overall, then, FIG. 2 shows the transition from individual endotoxinmoieties which are embedded in detergent micelles and, due to theirindividualization in these micelles, remain masked, to a scenario inwhich the individual moieties of endotoxin have been forced to aggregateso as to become detectable. That is, previously masked endotoxin inpanel (a) has been unmasked in panel (c), thereby allowing one todetermine that a solution previously thought (in panel (a)) to be freeof endotoxin actually contains this contaminant (panel (c)).

Unmasking Endotoxin Masked by a Detergent Masker with a Multi-ComponentModulator System in Combination with an Agent which Influences HydrogenBonding Stability in Solution

In the scenarios depicted in FIGS. 1 and 2, the solution conditions weresuch that use of a modulator system alone suffices to disrupt maskingdetergent micelles. Looked at another way, neither of the maskingmicelles of detergent shown in FIGS. 1 and 2 have been so stable as toresist disruption using a disrupting modulator alone. In addition, theconditions in FIGS. 1 and 2 have also been such that the equilibriabetween the solubilized and aggregated forms of endotoxin lay toward theaggregated form, so that detection of this aggregated form was possibleunder the solution conditions shown without any further measures needingto be taken.

The conditions underlying the scenario shown in FIG. 3 are nowdifferent. Here, individual molecules of endotoxin are inserted in thelipid layer of detergent micelles (again symbolized by a ring of opencircles representing the individual detergent molecules), but whetherdue to solution conditions, the nature of the interaction of the maskingdetergent with the endotoxin, or a combination of these things, theendotoxin inserted in the detergent micelle in panel (a) is more stable,and therefore less resistant to disruption with disrupting modulator,than either of the initial situations in FIGS. 1 and 2. Additionalmeasures are required to destabilize the detergent-endotoxin complex sothat, once destabilized, the modulator system can disrupt the micelleand liberate the inserted endotoxin.

To this end, the scenario shown in FIG. 3 entails using an agent whichinfluences hydrogen bonding stability in solution, symbolized by smallsquares added above the equilibrium arrows between panels (a) and (b),and shown in their interaction with the micelle-endotoxin complex inpanel (b). As mentioned above, one substance useful as an agent whichinfluences hydrogen bonding stability in solution is divalent calcium.

With the complex between the detergent masker and the masked endotoxinthus destabilized, a modulator system comprising both an adsorbingmodulator and a displacing modulator is added (see above equilibriumarrows between panels (b) and (c)) to displace the endotoxin from thealready destabilized micelle of masking detergent. As mentioned above,the displacing modulator may be sodium-dodecyl sulfate (SDS), itself adetergent. The possibility that the modulator system contains acomponent which is itself a detergent and which may form new micelles ofits own, is represented in panel (c) of FIG. 3 by a dotted circle, inwhich the endotoxin is inserted. Under the conditions prevailing in FIG.3, however, any micelle formed by the displacing modulator is not asstable as the micelle formed by the masking detergent shown in panel(a). This is at least partly because the adsorbing modulator, e.g. BSAshown in FIG. 3 also binds the displacing modulator on its surface,establishing an equilibrium between protein-bound and micelle-formingpopulations of the displacing modulator which effectively destabilizesany micelle formed by the displacing modulator.

The presence of a disrupting and reconfiguring modulator, for instance anon-micelle-forming amphiphilic species such as 1-dodecanol, is shownover the equilibrium arrows between panels (c) and (d) of FIG. 3. Theremainder of the schematic shown in FIG. 3 is analogous to what hasalready been discussed in detail above in the context of FIGS. 1 and 2.Briefly, the disrupting and reconfiguring modulator shown between panels(c) and (d) of FIG. 3 liberates and solubilizes endotoxin transientlyinserted in micelles formed by the displacing modulator, at the sametime establishing an equilibrium between solubilized (non-detectable)and aggregated (detectable) endotoxin species. This equlibrium may beshifted to the right (toward aggregated form) by the agent whichinfluences hydrogen bonding stability in solution (e.g. a salt with acation, preferably a divalent cation and/or a chaotropic agent).

Overall, FIG. 3 shows the liberation of a masked molecule of endotoxinfrom a stable complex with a micelle of a detergent masker. It uses anagent which influences hydrogen bonding stability in solution todestabilize this complex, and a multicomponent modulator which in totaldisrupts this complex and chaperones the liberated endotoxin through aseries of energetic minima in the ultimate direction of an aggregatedand therefore detectable complex of endotoxin.

Unmasking Endotoxin Masked by a Protein Masker with a Dual-ComponentModulator Comprising a Displacing Modulator and a Disrupting andReconfiguring Modulator

FIG. 4 is a schematic depiction of a scenario in which an endotoxin ismasked by a protein in solution. This is shown in panel (a) of FIG. 4.In the scenario depicted in FIG. 4, the protein, which may for examplebe an API in a pharmaceutical formulation, exhibits a binding cleftwhich is both sterically and electrostatically suitable to stably bindendotoxin. In this way, the protein masker binds molecules of endotoxin,rendering them undetectable. Addition of a modulator component,symbolized by the displacing modulator added above the equilibriumarrows between panels (a) and (b) of FIG. 4, displaces the endotoxinfrom its binding site on the protein masker. This displacing modulatormight for instance be a “second heteroatom-substituted aliphaticcomprising 8 to 16 carbon atoms” as discussed above. In the event thatthe displacing modulator would be e.g. sodium dodecyl sulfate, thisdisplacing modulator might bind to the surface of the masking protein,displacing the molecule of endotoxin from its stable binding positionwithin the protein's binding cleft. This is shown in the left portion ofpanel (b) of FIG. 4. In addition, as symbolized by the dotted circle inthe right portion of panel (b), the displacing modulator component mayalso form transient micelles of its own, essentially chaperoningendotoxin liberated from the protein masker in a form stably insertedinto the micelle's lipid layer. The exact position of the equilibriumshown in panel (b) of FIG. 4 depends on the effectiveness with which thedisplacing modulator binds to the surface of the masking protein (leftportion of panel (b)), as well as the stability of the micelle formed(right portion of panel (b)).

Regardless of the exact position of this equilibrium, the importantthing is that the displacing modulator depicted above the equilibriumarrows between panels (a) and (b) of FIG. 4 tends to liberate theendotoxin from its energetically stable binding position in or on themasking protein.

Once this endotoxin is freed from its masked state in or on the maskingprotein, a further modulator component (disrupting and reconfiguringmodulator), depicted above the equilibrium arrows between panels (b) and(c) of FIG. 4 shifts the energetic relationships prevailing in solutionsuch that the most stable state for endotoxin is in freely solubilizedform, chaperoned in solution by the disrupting and reconfiguringmodulator. This disrupting and reconfiguring modulator may for examplebe a “first heteroatom-substituted aliphatic comprising 8 to 16 carbonatoms” as discussed above, which may for example be 1-dodecanol. Asdiscussed above, this disrupting and reconfiguring modulator willtypically have the property of disrupting existing micelles (for exampleformed by the displacing modulator, and show in the right portion ofpanel (b)), while not forming micelles of its own. With any previousmicelles of the displacing modulator thus disrupted, and with thedisrupting and reconfiguring modulator unable to form correspondingmicelles of its own, the most energetically stable form of the endotoxinbecomes the solubilized form shown in panel (c) of FIG. 4, chaperoned bythe disrupting and reconfiguring modulator.

The remainder of FIG. 4 is as previously discussed for the finalequilibrium step in FIGS. 1 and 3. Briefly, there exists an equilibriumbetween individual, solubilized endotoxin (panel (c)) and aggregatedendotoxin (panel (d)). To the extent that any appreciable population ofaggregated endotoxin exists as part of this equilibrium, the endotoxinbecomes detectable where, stably bound in or on the masking protein, itpreviously was not. Overall, endotoxin which was previously masked inindividualized form by a protein has been unmasked and rendereddetectable by adjusting the solution conditions such that the mostenergetically favorable state in which endotoxin can reside becomes itsdetectable aggregated form. As in previous figures discussed above,then, the “unmasking” is the result of manipulating solution conditionsso as to shift equilibrium from a state in which endotoxin is stabilizedin individualized form (“masked”) toward a state in which endotoxin isaggregated and detectable (“unmasked”).

Unmasking Endotoxin Masked by a Protein Using a Multi-ComponentModulator Comprising an Adsorbing Modulator (Protein), a DisplacingModulator and a Disrupting/Reconfiguring Modulator, in Combination withan Agent which Influences Hydrogen Bonding Stability

The initial scenario shown in FIG. 5 corresponds to that shown in FIG.4: endotoxin is stably bound in or on a protein present in thecomposition. This protein in the composition, which may for example bean API, thus functions as an “endotoxin masker”. As already discussed inthe context of the scenario depicted in FIG. 3, the endotoxin is sostably complexed with the endotoxin masker in panel (a) of FIG. 5 thatsimple addition of modulator cannot alone liberate it. In FIG. 3,discussed above, the endotoxin masker was a detergent, which formed amicelle in which a single molecule of endotoxin was very stablyinserted. Now in FIG. 5, the endotoxin masker is a protein with abinding site amenable for stable endotoxin binding. But the principleremains the same: Whether inserted in the lipid layer of a detergentmicelle (FIG. 3) or residing stably in or on a protein, the endotoxin isstabilized to an extent that simple addition of a modulator is unable toovercome and the thus solubilized endotoxin remains undetectable.

As explained above for FIG. 3, this stable complex between endotoxin andendotoxin masker can be destabilized by addition of an agent whichinfluences hydrogen bonding stability in solution, for example a salt ora chaotropic agent, for example divalent calcium. This agent whichinfluences hydrogen bonding stability is symbolized in FIG. 5 by smallsquares starting over the equilibrium arrows between panels (a) and (b).This agent disrupts the hydrogen bonding network which is assumed toexist between endotoxin and the protein masker, thus raising the freeenergy of the complex to a level where the modulator components, whichare shown above the equilibrium arrows between panels (b) and (c), canbreak up the complex to such an extent that the endotoxin is dislodgedfrom the masking protein.

Using a modulator system comprising both an adsorbing modulator(protein) and a displacing modulator as shown in FIG. 5 then is assumedto lead to the equilibrium situation shown in panel (c). In the leftportion of panel (c) is the masking protein, now divested of theendotoxin previously bound. Molecules of the agent which influenceshydrogen bonding stability in solution as well as of the displacingmodulator, for example SDS, are shown bound to the surface of themasking protein, including in the binding site where endotoxin waspreviously bound. This depiction is intended to represent the fact thatthe displacing modulator effectively displaced endotoxin from its stableposition in or on the masking protein. The middle portion of panel (c)of FIG. 5 shows a micelle which might be formed by the displacingmodulator (e.g. SDS), with a molecule of endotoxin transiently insertedinto the lipid layer of the micelle. Molecules of the agent whichinfluences hydrogen bonding stability in solution are also shown boundto endotoxin and micelle, and serve to further destabilize this micelle,ensuring that the micelle in fact remains transient and does not presentthe endotoxin with an energy binding minimum from which it cannot bedislodged by a further disrupting modulator. Finally, the right portionof panel (c) shows the adsorbing modulator (protein) acting, asdescribed briefly above, as a “molecular sponge” which adsorbs both theagent which influences hydrogen bonding stability in solution as well asthe displacing modulator on its surface. This effectively depletes thesespecies in solution, destabilizing the transient micelle shown in themiddle portion of panel (c) to the extent that the displacing modulatoris depleted, while stabilizing it to the extent that the agent whichinfluences hydrogen bonding stability in solution is depleted.Generally, however, the amount of the agent which influences hydrogenbonding stability in solution will be high enough to destabilize theinitial complex between masking protein and endotoxin that enough ofthis agent will persist in solution despite depletion by the adsorbingmodulator, so that the transient micelle shown in panel (c) will bedestabilized as desired.

Use of a disrupting and reconfiguring modulator, for example as shownover the equilibrium arrows between panels (c) and (d) of FIG. 5 (e.g.1-dodecanol), will then break up the transient micelle shown in panel(c) so as to liberate the molecule of inserted endotoxin. As alreadydiscussed above the thus solubilized endototoxin (panel (d)) will thenenter into an equilibrium relationship with a reconfigured, aggregatedform of endotoxin (panel (e)) which can be detected as discussed above.

Unmasking Endotoxin Masked by Both Protein and Detergent Maskers with aMulti-Component Modulator Comprising an Adsorbing Modulator (Protein), aDisplacing Modulator and a Disrupting/Reconfiguring Modulator, inCombination with an Agent which Influences Hydrogen Bonding Stability inSolution

Many protein APIs, for example, antibodies, antibody fragments,hormones, enzymes, fusion proteins or protein conjugates are formulatedand marketed at such high concentrations that detergents must beincluded in solution to avoid unwanted protein aggregation. The initialscenario shown in FIG. 6 is thus representative of one of the mostrelevant situations in the field of pharmaceutical formulation becauseboth detergent and protein (e.g. API protein) maskers are present. Themolecule of endotoxin is shown as inserted in the lipid layer of adetergent micelle (again symbolized by a ring of open circlesrepresenting the individual detergent molecules) as well as bound in oron the masking protein. In reality, these two species are likely toexist in equilibrium, with the relative position of this equilibrium,toward either a micelle- or a protein-bound species of endotoxin, beingdictated by the relative stability of the respective complexes. Allother things being equal, the complex of lower free energy, andtherefore greater stability will generally prevail.

The discussion of FIG. 6 is analogous to that of FIG. 5 above, with theonly difference being that panel (b) of FIG. 6 shows both the protein-and micelle-bound species of endotoxin in mutual equilibrium, eachdestabilized by the agent which influences hydrogen bonding stability insolution. Using an adsorbing modulator and a displacing modulator leadsto the equilibrium situation depicted in panel (c) of FIG. 6. Thediscussion above for panel (c) of FIG. 5 applies here correspondingly.The use of a further disrupting and reconfiguring modulator (shown overthe equilibrium arrows between panels (c) and (d)) which is capable ofdisrupting the transient micelle of panel (c) without forming micellesof its own, frees the endotoxin from its transiently bound state in amicelle of displacing modulator (middle portion of panel (c)), andengenders the equilibrium relationship between soluble (non-detectable)and aggregated (detectable) forms of endotoxin as discussed above. Asexplained above for previous figures, the disrupting and reconfiguringmodulator shown in panel (d) is shown in equilibrium between statesbound to the liberated endotoxin (upper portion of panel (d)) anddetergent previously constituting the detergent micelle shown in panel(a) (lower portion of panel (d)).

It should be noted that the above scenarios are intended to illustratethe principles which the present inventors believe underlie theadvantageous unmasking effect of the present invention in differentsituations. From the illustrative FIGS. 1-6, it will be clear that theprocesses discussed are all equilibrium processes, and that there isaccordingly no prerequisite for the order of addition of differentcomponents of the modulator system or, if used, of the agent influencinghydrogen bonding stability and solution. The equilibria shown will thusbe automatically established as soon as the components are presenttogether in solution. The “order” of addition of these components asimplied in the discussion above and shown in FIGS. 2-6 thus servesmerely to illustrate the mechanisms which the present inventors believeunderlie the advantageous technical effect of the present invention.Accordingly, unmasking a previously masked endotoxin might beaccomplished by adding components at separate points in time assuggested by FIGS. 2-6, however the desired unmasking effect is alsoachievable when the components depicted in FIGS. 2-6 are added all atonce.

In the most general sense, the scenarios depicted above in FIGS. 1-6 andthe corresponding discussion should illustrate the following generalprinciples, which are intended as general guidelines to the skilledperson in implementing the present invention. Many solutions which testnegative for endotoxin by conventional methods actually containendotoxin in masked form. Conventional methods detect endotoxin in itsaggregated form, so the fact that many existing solutions, such aspharmaceutical formulations, test negative for endotoxin does notnecessarily mean that these solutions contain no endotoxin, but ratherthat they contain no endotoxin in detectable form.

In their most general form, the methods of the invention allow unmaskingof endotoxin, e.g. by destabilizing complexes between endotoxin andendotoxin maskers so as to liberate, and ultimately aggregate individualmolecules of endotoxin, thus rendering previously undetectable endotoxindetectable. Liberation of endotoxin from its masked complexes withendotoxin maskers may ensue directly using a disrupting andreconfiguring modulator to break up such complexes or, for especiallystable complexes, these may be destabilized and then broken up with sucha modulator or with a multi-component modulator system. However thebound endotoxin is liberated, the net effect is that endotoxintransitions from a stably bound form into a transient soluble form whichmay then aggregate. In its broadest sense, then, the methods of thepresent invention entail adjusting solution conditions as describedabove so as to usher previously masked endotoxin through a series ofequilibria, wherein the final transition results in aggregation ofendotoxin in a form which is detectable.

Since the unmasking and/or detection of endotoxin according to themethods described herein depend on a final reconfiguration of liberatedendotoxin in solubilized (undetectable) form into aggregated form(detectable) a reconfiguring modulator will generally be needed. Thisreconfiguring modulator (e.g. 1-dodecanol) will generally have thecharacteristic of not forming micelles on its own, while stabilizingindividual molecules of endotoxin such that these can enter into anequilibrium with aggregated forms of endotoxin. As is clear from theabove, a reconfiguring modulator will sometimes, but need notnecessarily, also function as a disrupting modulator which is able tobreak up an initial complex between endotoxin and a micelle of maskingdetergent and/or a complex of between endotoxin and a transient micelleof displacing modulator.

The following examples, including the experiments conducted and theresults achieved, are provided for illustrative purposes only and arenot construed as limiting the present invention.

EXAMPLES

Introduction

Endotoxin masking is a common phenomenon in pharmaceutical composition,especially biopharmaceutical drug products. Masking of endotoxin isdriven by several factors, leading in the end to the non-detectabilityor at least a decreased detectability of the endotoxin in the drugproduct.

In one scenario, masking is not caused by the active pharmaceuticalingredient (API), e.g. protein, itself but by the formulationingredients. Such ingredients are detergents, which are added to preventaggregation of the protein, and buffer substances like citrate,phosphate, Tris, acetate, histidine, glycine which are added forpH-adjustment of the product.

Unsurprisingly, the kinetics of masking is influenced by temperature,with masking proceeding faster at higher temperatures than at lowertemperatures. Unless otherwise specified, all experiments describedbelow were performed at room temperature. This is the temperature atwhich production process steps of the active pharmaceutical ingredient(API) are often performed, and is therefore the most relevanttemperature for assessing the applicability of the inventive methodsdescribed herein to industrial processes.

Example 1: Unmasking of Endotoxin from a Masking System of Polysorbate20/Citrate Using a Disrupting and Reconfiguring Modulator (1-Dodecanol)Alone, and Together with a Further Adsorbing Modulator (BSA)

A masking system of polysorbate 20/citrate was chosen for the firstexperiment because citrate and polysorbate 20 are often included inbiopharmaceutical formulations. These experiments are intended todetermine whether masked endotoxin can be released from a complex withdetergent masker by addition of a disrupting and reconfiguring modulatoras described herein.

Materials and Methods

Endotoxin masking was performed as follows. 1 ml aqueous aliquots of 10mM Citrate pH 7.5 containing 0.05% (w/v) of polysorbate 20 were preparedin endotoxin-free glass test tubes. Subsequently, 10 μl of a 10,000EU/ml LPS stock solution (LPS 055 B5, Sigma L2637-5MG) were added, theresulting solution was vortexed for 1 min and was stored at roomtemperature for at least 24 hours. As a positive LPS control containingnon-masked LPS, 10 μl of a 10,000 EU/ml LPS stock solution was added to1 ml of endotoxin-free water, mixed and identically incubated as themasking preparations, but without polysorbate 20. The LPS-water positivecontrol is described in more detail below.

Endotoxin unmasking was performed as follows. 100 μl of stock solutionsof each of 1-dodecanol (disrupting and reconfiguring modulator)dissolved in 100% ethanol and 100 mg/ml BSA (adsorbing modulator)dissolved in endotoxin-free water were added. 1-dodecanol and BSA areused here as the two components of a dual-component modulator system. Aseparate unmasking experiment was performed identically as above, exceptthat a single-component modulator was used. The single modulator in thisexperiment was 1-dodecanol alone, i.e. without BSA. Concentrations ofthe 1-dodecanol stock solutions were 400, 200, 100, 50, 25, 12.5 and6.25 mM. For unmasking, the unmasking stock solutions of BSA and1-dodecanol were sequentially added with 2 minutes mixing by vortexingafter each addition. After mixing, the samples were incubated for 30minutes at room temperature without mixing.

Endotoxin content was analyzed using EndoLISA® (Hyglos GmbH) accordingto the kit instructions. Sample dilutions were 1:10 and 1:100 inendotoxin-free water.

Endotoxin recovery was calculated as a percentage of recovery of aseparate LPS-water control containing only water and LPS without anymasking component. In the absence of any endotoxin masker, no LPS inthis LPS.water control should be masked, that is all LPS present in thisLPS-water control should be detectable. In this way, the LPS-watercontrol serves as a standard to determine both qualitatively as well asquantitatively whether the EndoLISA® detection kit employed isfunctioning properly to detect LPS (qualitative control), and whetherall LPS known to be present in the control is in fact detected(quantitative control).

Results

The recovery data in FIG. 7 and Table 1 (below) show that by theaddition of BSA and/or 1-dodecanol in concentrations from 20 to 2.5 mM,masked endotoxin can be recovered to an extent greater than 100%. In theabsence of BSA, 100% recovery cannot be achieved but, rather, greaterthan 50% in the range of 10 to 2.5 mM of 1-dodecanol with maximumrecovery at 5 mM 1-dodecanol of approximately 90%.

In this and following examples, recoveries of greater than 100% of LPSshould be interpreted in light of the following: The activity of LPS hasbeen found to depend on both LPS form (e.g. extent and orientation ofaggregation) as well as LPS structure (this structure varying slightlyin LPS deriving from different bacterial species). The inventiveunmasking methods described herein have the potential to alter both theform and the orientation of LPS aggregation (indeed, it is due to suchalteration as promoted by the modulator, especially the reconfiguringmodulator, that unmasking of LPS is possible at all). The change in formand orientation of LPS aggregation between the LPS-water control (notunmasked) and the unmasked samples may in some cases cause the activitydetected following unmasking to exceed that measured in the positiveLPS-water control. This does not mean that performing the inventiveunmasking methods as described herein generates new LPS not previouslypresent, but rather than in some cases, performing the inventiveunmasking methods as described herein alter the form of existing LPSsuch that the apparent measured activity for a given amount of LPSincreases.

TABLE 1 1-Dodecanol (mM) BSA (mg/ml) % LPS recovery 40 — 28 20 — 46 10 —60 5 — 89 2.5 — 65 1.25 — 31 0.625 — 7 40 10 70 20 10 157 10 10 186 5 10170 2.5 10 134 1.25 10 71 0.625 10 0

The results clearly demonstrate that masked endotoxin can be unmasked bythe addition of the modulator 1-dodecanol (disrupting and reconfiguringmodulator) alone. The results further show that this unmasking effectcan be improved by the addition of a further adsorbing modulator (BSA).In this latter case in which 1-dodecanol and BSA are added as adual-component modulator, the BSA helps to adsorb detergent, thusdestabilizing the detergent micelle masking the endotoxin, the modulator1-dodecanol, is capable of disrupting detergent micelles (in itscapacity as disrupting modulator) and reconfiguring liberated endotoxininto an aggregate structure (in its capacity as reconfiguringmodulator). In the case of polysorbate 20 in the absence of BSA analmost quantitative recovery is possible (89% at 5 mM 1-dodecanol). Thismay be due to the similarity in the length of the alkyl chains of1-dodecanol and the LPS-masking detergent polysorbate 20. The unmaskingis improved by the addition of BSA, which is assumed to shift theequilibrium of LPS from solubilized to aggregated form (see e.g. FIG.2).

Example 2: Unmasking of Endotoxin from a Masking System of Polysorbate20/Citrate Using Alcohols of Different Alkyl Chain Length as Disruptingand Reconfiguring Modulators

This experiment investigates the use of various alkyl alcohols asdisrupting and reconfiguring modulators. One aim of the experimentsdescribed in this example was to investigate the relationship betweenalkyl chain length in the alcohol and unmasking efficiency. To this end,unmasking was performed by the addition of alcohols with carbon atomchain lengths from C8-C18 in different concentrations.

Materials and Methods

Endotoxin masking was performed as described in Example 1. Unmasking wasperformed by the addition of stock solutions of unbranched 1-alcohols ofdifferent alkyl chain lengths (C₈, Co, C₁₂, C₁₄, C₁₆, C₁₈) as modulators(disrupting and reconfiguring modulators) as described in Example 1 for1-dodecanol (having a 12-carbon alkyl chain). Each of the stocksolutions was dissolved in 100% ethanol. In contrast to certain of theexperiments described above in Example 1, no other modulator components,e.g. BSA, were included in the present unmasking experiments. Analysisof endotoxin concentrations was performed using the EndoLISA® kit(Hyglos GmbH), and the subsequent calculation of endotoxin recovery wasexpressed as a percent of the LPS in the LPS-water control sample. TheLPS-water positve control is explained in detail in Example 1, above.

Results

Table 2 (below) show the percentage of unmasked endotoxin as dependenton alcohol concentration and the length of the alkyl chain in thealcohol.

TABLE 2 % LPS Recovery 1- 1- Conc. 1- 1- 1- 1- Hexa- Octa- (mM) OctanolDecanol Dodecanol Tetradecanol decanol decanol 40 0 0 28 10 nd nd 20 0 046 36 1 1 10 0 0 60 44 3 1 5 0 1 89 28 3 0 2.5 0 5 65 16 0 3 1.25 0 1 3125 0 1 0.625 1 4 7 10 2 1 nd = no data

Endotoxin recoveries of, i.e. unmasking endotoxin by, greater than 40%were achieved using 1-dodecanol and 1-tetradecanol. Recoveries usingalcohols with alkyl chains lengths below or above C12 and C14 are below10%.

The above results imply that the alkyl chain length of the alcohol usedas a disrupting and reconfiguring modulator should ideally match thealkyl chain length of the acyl chains in the endotoxin as closely aspossible. In the present case, the lengths of the acyl chains in theLipid A component of LPS are C12 and C14, and it was the 1-alcoholshaving alkyl chain lengths in that range which, when used as disruptingand reconfiguring modulators, most effectively unmasked the endotoxin.

Example 3: Unmasking of Endotoxin from Masking Systems of VariousNon-Ionic Surfactants Using 1-Dodecanol as a Disrupting andReconfiguring Modulator Alone, and Together with the Adsorbing ModulatorBSA

To investigate the hypothesis that unmasking endotoxin from polysorbate20 by 1-dodecanol alone is promoted by equivalent or similar alkyl chainlength of the masking surfactant and 1-dodecanol, various experimentswere designed using masking detergents of different chain lengths anddifferent structure, and these were then unmasked using a disrupting andreconfiguring modulator of fixed alkyl chain length (1-dodecanol, with aC₁₂ alkyl chain). To this end, masked samples were prepared inpolysorbate 80 and TRITON™ (non-ionic surfactant) X-100 and these weresubsequently unmasked with 1-dodecanol or BSA/1-dodecanol usingdifferent concentrations of 1-dodecanol.

Materials and Methods

Endotoxin masking was performed as follows: 1 ml aliquots of 10 mMcitrate pH 7.5 containing 0.05% of polysorbate 20, polysorbate 80 orTRITON™ (non-ionic surfactant) X-100 were prepared in endotoxin-freeglass test tubes. Subsequently, 10 μl of a 10,000 EU/ml LPS stocksolution (LPS 055 B5, Sigma L2637-5MG) were added, vortexed for 1 minand stored at room temperature for at least 24 hours. As a positive LPScontrol, 10 μl of a 10,000 EU/ml LPS stock solution was added to 1 ml ofendotoxin-free water, mixed and identically incubated as the maskingpreparations. The positive LPS-water control is discussed in detailabove in Example 1.

Unmasking was performed by the addition of stock solutions of1-dodecanol (as a disrupting and reconfiguring modulator) in differentconcentrations as described in Example 1. Stock solutions of therespective alcohols were dissolved in 100% of ethanol. Unmasking wasperformed in both the absence and presence of 10 mg/ml BSA as describedin Example 1. Analysis of endotoxin concentrations was performed withthe EndoLISA® kit (Hyglos GmbH), with subsequent calculation of recoveryof endotoxin expressed as a percent of the endotoxin in the LPS/watercontrol sample.

Results

Table 3 (below) shows the recoveries of LPS after unmasking from therespective polysorbate 20/citrate, polysorbate 80/citrate and TRITON™(non-ionic surfactant) X-100/citrate masking systems as dependent on the1-dodecanol (disrupting and reconfiguring modulator) concentration inthe absence or presence of BSA (adsorbing modulator).

TABLE 3 Dodecanol BSA % LPS recovery (mM) (mg/ml) Polysorbate 20Polysorbate 80 Triton X-100 40 — 28.0 4.9 nd 20 — 46.2 7.5 3.4 10 — 60.511.5 nd 5 — 89.1 25.2 0.0 2.5 — 64.9 28.5 nd 1.25 — 31.2 12.1 0.0 0.625— 7.2 0.0 nd 0.313 — nd nd 0.0 40 10 69.7 19.4 nd 20 10 156.8 36.4 2.010 10 186.1 69.9 nd 5 10 170.5 86.9 23.0  2.5 10 133.5 94.2 nd 1.25 1071.3 2.9 0.0 0.625 10 0.0 12.9 nd 0.313 10 nd nd 0.0 nd = no data

Unmasking with 1-dodecanol from the polysorbate 80/citrate maskingsystem results in recovery of approximately 30% at an optimalconcentration of 1-dodecanol of 2.5 mM. In the presence of BSA up to 90%can be recovered. Both unmasking approaches from the TRITON™ (non-ionicsurfactant) X-100 masking system (i.e. with and without BSA) result inLPS recoveries below 20%, regardless of the concentration of1-dodecanol.

Thus, unmasking using 1-dodecanol alone (as a disrupting andreconfiguring modulator) is sufficient to unmask LPS from maskingsystems such as in the polysorbate 20 masking system. The addition ofBSA (as an adsorbing modulator) to adsorb the masking detergent improvesunmasking recoveries in the polysorbate 20 and polysorbate 80 maskingsystems. Unmasking from the TRITON™ (non-ionic surfactant) X-100 systemis not highly efficient even when BSA is added together with1-dodecanol. Adding a further modulator component such as e.g. SDS (as adisplacing modulator) can help improve recovery of LPS from TRITON™(non-ionic surfactant)-X-100 masking formulations.

Example 4: Increasing Unmasking Efficiency by Addition of a Modulatorand a Chaotropic Agent which Influences Hydrogen-Bonding Stability

The weak recovery of LPS from the TRITON™ (non-ionic surfactant) X-100masking system using the dual-modulator system of BSA (adsorbingmodulator) and 1-dodecanol (disrupting and reconfiguring modulator) maybe due to the high stability of the complex formed by TRITON™ (non-ionicsurfactant) X-100 and LPS. This high stability may prevent the desireddestruction of the endotoxin-masking micelles of TRITON™ (non-ionicsurfactant) X-100 by the disrupting action of 1-dodecanol and adsorptionof the detergent by BSA.

For this reason, the present experiments investigate the possibility ofdestabilizing the masking complex by addition of a chaotropic salttogether with a multi-component modulator. The hope was that bydestabilizing an otherwise stable detergent micelle, destruction of thismicelle using a multi-component modulator system of 1-dodecanol (asdisrupting and reconfiguring modulator), BSA (as adsorbing modulator)and SDS (as displacing modulator) would then become possible.

Materials and Methods

Endotoxin masking was performed as follows: 1 ml aliquots of 10 mMcitrate pH 7.5 containing 0.05% of TRITON™ (non-ionic surfactant) X-100were prepared in endotoxin-free glass test tubes. Subsequently, 10 μl ofa 10,000 EU/ml LPS stock solution (LPS 055 B5, Sigma L2637-5MG) wereadded, vortexed for 1 min and stored at room temperature for at least 24hours. As a positive LPS control, 10 μl of a 10,000 EU/ml LPS stocksolution was added to 1 ml of endotoxin free water, mixed and incubatedin an identical manner as the masking preparations. The positiveLPS-water control is discussed in detail above in Example 1.

Unmasking endotoxin was performed as follows: 100 μl of the followingstock solutions were added as single component or as combinations to the1 ml masked samples: 1 M CaCl₂ (dissolved in water), 100 mg/ml BSA(dissolved in water), 1% SDS (dissolved in water) and 50 mM 1-dodecanol(dissolved in 100% ethanol). In the case of addition of combinations,the agents were added sequentially, with a 2-minute vortexing stepbetween each addition. The samples were then incubated at roomtemperature for 30 minutes without shaking.

Endotoxin content was analyzed using the EndoLISA® kit (Hyglos GmbH)according to the kit instructions. Sample dilutions were 1:10 and 1:100in endotoxin-free water. Endotoxin recovery was calculated and expressedas a percentage of recovery of the LPS-water control. The positiveLPS-water control is discussed in detail above in Example 1.

Results

FIG. 8 shows the percentage of LPS recovery as dependent on the additionof combinations of CaCl₂ (C), BSA (B; adsorbing modulator), SDS (S;displacing modulator) and 1-dodecanol (D; disrupting and reconfiguringmodulator). 1-Dodecanol as the sole (disrupting and reconfiguring)modulator does not efficiently unmask LPS from a TRITON™ (non-ionicsurfactant) X-100 masking complex. Addition of BSA (adsorbing modulator)and 1-dodecanol (disrupting and reconfiguring modulator) as adual-component modulator system results in approximately 20% recovery.Further addition of either a chaotropic salt such as CaCl₂ or a furthermodulator such as SDS (displacing modulator) does not result in LPSrecoveries greater than 20%. However, the addition of CaCl₂, BSA(adsorbing modulator), SDS (displacing modulator) and 1-dodecanol(disrupting and reconfiguring modulator) results in LPS recoveries ofgreater 100%.

Thus, additionally to BSA (adsorbing modulator) and 1-dodecanol(disrupting and reconfiguring modulator), a chaotropic salt and afurther displacing modulator such as the detergent SDS help to break upthe TRITON™ (non-ionic surfactant) X-100 masking complex. In this way,the combination of these 4 additives seems to break apart the maskingcomplex and allows the formation of detectable LPS.

Example 5: Comparison of Different Unmasking Approaches from VariousMasking Systems

As efficient unmasking from the TRITON™ (non-ionic surfactant) X-100masking system was observed using a combination of CaCl₂, BSA, SDS and1-dodecanol, the question of unmasking efficiency of this approachstarting from polysorbate masking systems remains. To answer thisquestion, endotoxin was masked in polysorbate 20, 80 and TRITON™(non-ionic surfactant) X-100/citrate masking systems and subsequentlyunmasked using 1-dodecanol alone; BSA and 1-dodecanol in combination; orCaCl₂, BSA, SDS and 1-dodecanol in combination. In these experiments,1-dodecanol is used as a disrupting and reconfiguring modulator, BSA isused as an adsorbing modulator, SDS is used as a displacing modulatorand CaCl₂ is used as an agent which influences hydrogen-bondingstability in solution.

Materials and Methods

Endotoxin masking was performed as follows: 1 ml aliquots of 10 mMcitrate pH 7.5 containing either 0.05% polysorbate 20, or 0.05%polysorbate 80 or 0.05% TRITON™ (non-ionic surfactant) X-100 wereprepared in endotoxin-free glass test tubes. Subsequently, 10 μl of a10,000 EU/ml LPS stock solution (LPS 055 B5, Sigma Aldrich L2637-5MG)were added, vortexed for 1 min and stored at room temperature for atleast 24 hours. As a positive LPS control, 10 μl of a 10,000 EU/ml LPSstock solution were added to 1 ml of endotoxin-free water, mixed andidentically incubated as the masking preparations. The function of thepositive LPS-water control is as described above in Example 1.

Unmasking of endotoxin was performed as follows: Either 100 μl of a 50mM 1-dodecanol stock solution; or 100 μl of 100 mg/ml BSA and 100 μl ofa 50 mM 1-dodecanol stock solution; or 100 μl of a 1 M CaCl₂ solution,100 ml of a 100 mg/ml BSA solution, 100 μl of a 1% SDS solution and 100μl of a 50 mM 1-dodecanol solution were added to the solution containingmasked LPS. In the case of addition of combinations, the agents wereadded sequentially with a 2-minute vortexing step between each addition.The samples were then incubated at room temperature for 30 minuteswithout shaking.

Endotoxin content was analyzed using the EndoLISA® kit (Hyglos GmbH)according to the kit instructions. Sample dilutions were 1:10 and 1:100in endotoxin-free water. Endotoxin recovery was calculated as apercentage of recovery of the LPS-water control.

Results

Table 4 (below) and FIG. 9 show the percentages of LPS recovery usingeither 1-dodecanol alone; BSA and 1-dodecanol in combination; or CaCl₂,BSA, SDS and 1-dodecanol in combination (CBSD) for unmasking fromvarious detergent masking systems.

TABLE 4 % LPS recovery Masking detergent 1-dodecanol BSA/1-dodecanolCBSD Polysorbate 20 78 170 141 Polysorbate 80 28 94 161 TRITON ™ (non- 023 168 ionic surfactant) X-100

Efficient (˜80%) unmasking from the polysorbate 20 masking system isachieved by 1-dodecanol, BSA/1-dodecanol and CaCl₂/BSA/SDS/1-dodecanol.In the case of a polysorbate 80 masking system, good unmaskingefficiency is achieved in the presence of BSA/1-dodecanol andCaCl₂/BSA/SDS/1-dodecanol. In the case of a TRITON™ (non-ionicsurfactant) X-100 masking system, the addition ofCaCl₂/BSA/SDS/1-dodecanol results in good LPS recovery.

Thus, dependent on the stability of the masking complex, efficientendotoxin recoveries can be achieved using different unmaskingapproaches. However, the unmasking approach involving the combination ofCaCl₂, BSA, SDS and 1-dodecanol may be the most universal method, due toits ability to achieve efficient unmasking, regardless of the maskingsystem used. As is clear from the experiments described herein above, anoptimal composition for unmasking LPS in any given formulation can beeasily achieved by routine experimentation.

Example 6: Unmasking of Endotoxin from Different Endotoxin Sources

Endotoxin unmasking experiments in Examples 1-5 were performed with acommercially available, highly purified LPS preparation of E. coliO55:B5. As only the conserved Lipid A part of LPS is responsible fortoxicity and for detectability in Factor C-based detection methods, itcan be assumed that the unmasking approaches described above will workequally well using LPS preparations from bacteria other than E. coliO55:B5. However, the literature also describes differences in acyl chainlength for the lipid A part of LPS, as well as modifications of sidechains. Even more, the length of the O-sugar side chains of LPS couldpotentially impact the unmasking approach. Furthermore, it cannot beexcluded that purified LPS and naturally occurring endotoxin (NOE) maydiffer in their unmasking behavior. To address these issues, and excludethe possibility, that the unmasking approaches are specific for the usedLPS of E. coli O55:B5, LPS from different bacteria, different length incore- and O-sugar chains and different purity were masked in variousdetergent masking systems and subsequently unmasked using either1-dodecanol alone, BSA/1-dodecanol or CaCl₂/BSA/SDS/1-dodecanol.

Materials and Methods

Masking of endotoxin was performed as follows: LPS samples of differenttypes and from different sources were (approximately 50 EU/mL) added to1 ml masking samples containing either 0.05% polysorbate 20, 0.05%polysorbate 80 or 0.05% TRITON™ (non-ionic surfactant) X-100 and 10 mMcitrate pH 7.5. LPS source, type and the supplier are shown in Table 5(below). NOEs were produced from bacterial culture supernatant aftergrowth to stationary phase in LB media by sterile filtration. As apreservative, 0.05% sodium azide was added. Lyophilized LPS wasdissolved in endotoxin-free water. LPS solutions for which the supplierin Tables 5-7 is indicated as “LMU” were kind gifts of Dr. A. Wieser ofthe Ludwig-Maximilian University of Munich. Endotoxin content of the LPSstock solutions was determined using the EndoZyme® kit (Hyglos GmbH) andstock solutions of approx. 5000 EU/ml LPS in endotoxin-free water wereproduced. From these solutions 10 μl were added to 1 ml masking samples.Afterwards, the samples were allowed to mask the respective LPS for 7days at room temperature.

Unmasking of endotoxin was performed by addition of 100 μl of either a100 mM 1-dodecanol stock solution, or addition of 100 μl of a 100 mg/mlBSA and 100 μl of 100 mM 1-dodecanol stock solution or by addition of100 μl of each of 1 M CaCl₂), 100 mg/ml BSA, 1% SDS and 100 mM1-Dodecanol solutions. Unmasking and determination of endotoxin contentwere performed as described in Examples 1-5.

Results

Tables 5-7 (below) show the percent of LPS recovery after masking andafter unmasking of LPS from different sources and typs out of differentdetergent masking systems. Specifically, Table 5 shows the resultsobtained for a masking system of TWEEN 20™ (polysorbate 20)/Citrate;Table 6 shows the results obtained for a masking system of TWEEN 80™(polysorbate 80)/Citrate; and Table 7 shows the results obtained for amasking system of TRITON™ (non-ionic surfactant) X-100/Citrate.

TABLE 5 Tween 20/Citrate masking system Masking CaCl₂/BSA/SDS/ controlDodecanol BSA/Dodecanol Dodecanol supplier (% recovery) (% recovery) (%recovery) (% recovery) Klebsiella LMU 0.0 66 128 212 pneumoniaMorganella LMU 0.0 81 110 120 morganii Yersinia LMU 0.0 63 174 243enterocolitica Serratia LMU 0.0 128 168 182 marcescens Neisseria LMU 0.09 23 38 meningitis Acinetobacter LMU 0.0 0 124 655 baumanni *Enterobacter Hyglos 0.0 55 156 187 cloacae (NOE) * Salmonella Sigma 0.042 63 76 enterica E. coli K 12 Invivogen 3.0 78 80 137 Pseudomonas Sigma0.0 14 5 179 aeruginosa * * Strains which are common water contaminants,and therefore more likely to be present in processes for the productionof pharmaceutical compositions

TABLE 6 Tween 80/Citrate masking system Masking CaCl₂/BSA/SDS/ controlDodecanol BSA/Dodecanol Dodecanol supplier (% recovery) (% recovery) (%recovery) (% recovery) Klebsiella LMU 0.0 12 173 353 pneumoniaMorganella LMU 15.0 15 39 99 morganii Yersinia LMU 7.0 22 168 309enterocolitica Serratia LMU 0.0 105 199 326 marcescens Neisseria LMU 0.00 11 42 meningitis Acinetobacter LMU 0.0 7 337 511 baumanni *Enterobacter Hyglos 24.2 27 74 183 cloacae (NOE) * Pseudomonas Sigma 1.01 1 90 aeruginosa * Salmonella Sigma 0.0 18 10 69 enterica E. coli K 12Invivogen 1.9 85 106 176 * Strains which are common water contaminants,and therefore more likely to be present in processes for the productionof pharmaceutical compositions

TABLE 7 Triton X-100/Citrate masking system Masking CaCl₂/BSA/SDS/control Dodecanol BSA/Dodecanol Dodecanol supplier (% recovery) (%recovery) (% recovery) (% recovery) Klebsiella LMU 9.8 22 12 162pneumonia Morganella LMU 5.5 35 23 48 morganii Yersinia LMU 0.0 13 19236 enterocolitica Serratia LMU 3.5 28 20 80 marcescens Neisseria LMU0.0 55 14 161 meningitis Acinetobacter LMU 7.8 0 57 918 baumanni *Enterobacter Hyglos 0.0 2 26 85 cloacae (NOE) * Pseudomonas Sigma 0.0 111 25 aeruginosa * Salmonella enterica Sigma 0.0 21 12 234 * Strainswhich are common water contaminants, and therefore more likely to bepresent in processes for the production of pharmaceutical compositions

The above data clearly show that the ability to successfully unmaskendotoxin from various masking systems is independent of the source andtype of LPS used. These results are important because they show that theunmasking methods of the present invention represent a general teachingapplicable to various types of endotoxin from various sources, under avariety of masking conditions.

Example 7: Unmasking of Endotoxin from Protein Masking Systems

The previous experiments have investigated the unmasking of LPS fromdetergent masking systems. However, as described herein above,detergents are not the only substances which can mask endotoxin fromdetection. Proteins (e.g. protein APIs) are also capable of maskingendotoxin from detection when they contain binding sites on or withintheir structure in which endotoxin can bind, thus evading detection. Thepresent experiments therefore relate to the masking of endotoxin (LPS)by a protein rather than a detergent. Lysozyme was used as the maskingprotein in these experiments because its ability to bind endotoxin isknown (see e.g. Ohno & Morrison (1999). J. Biol. Chemistry 264(8),4434-4441).

Materials and Methods

Endotoxin masking was performed as follows: 50 EU/ml of LPS (E. coliO55:B5) was incubated for seven days in 10 mM citrate buffer, pH 7.5containing 1 mg/ml hen egg white lysozyme (Sigma Aldrich) at roomtemperature.

Endotoxin unmasking was performed as follows: Unmasking was performed byaddition of unmasking reagents (modulators as described in previousexamples and agents influencing hydrogen bonding stability) in variouscombinations. Specifically, 100 μl of the following unmasking agentswere added to 1 ml aliquots of the masked samples: 1-dodecanol, CaCl₂,BSA, SDS. All stock solutions were dissolved in water except1-dodecanol, which was dissolved in 100% ethanol. The addedconcentrations of the stock solutions were 100 mM 1 M CaCl₂, 100 mg/mlBSA and 1% SDS, respectively. Unmasking was performed by sequentialaddition of the various components with a two-minute vortexing stepafter each addition. The samples were then incubated for 30 minutes atroom temperature and subsequently diluted 1:10 and 1:100 inendotoxin-free water for analysis using the EndoLISA® kit (Hyglos GmbH).

Results

Table 8 (below) shows the efficiency unmasking from a protein masker(lysozyme) as dependent on the added components.

TABLE 8 CaCl2 BSA SDS 1-dodecanol % recovery LPS − − − − 0 + − − − 0 + +− − 4 + + + − 33 + + + + 115 + + − + 15 + − + + 0 + − + − 4 + − − + 2− + − − 9 − + + − 0 − + + + 1 − + − + 6 − − + − 0 − − + + 0 − − − + 1

In the case of masking by lysozyme, use of 1-dodecanol (reconfiguringmodulator) alone or together with a supporting detergent (displacingmodulator) as a further component of the modulator system does notefficiently unmask. Here, the lysozyme-LPS masking complex seems to bemore stable due to electrostatic interactions between the negativelycharged LPS and the positively charged lysozyme. Improvement ofunmasking may be achieved by the addition of salt, which disrupts theelectrostatic interaction, thus rendering the lysozyme-LPS complex morelabile and increasing its susceptibility to disruption with modulator.To this end, good results may be achieved by using a multi-componentmodulator system of BSA (adsorbing modulator), SDS (displacingmodulator) and 1-dodecanol (reconfiguring modulator), together withCaCl₂ to lower the stability of the initial lysozyme-LPS complex. Thecombination of these components is able to break up the masking complexand lead to detectable LPS structures. This model may be taken as ageneral model of the measures which may be used to unmask endotoxin whenit is masked, in whole or in part, by a protein, e.g. a protein API in apharmaceutical composition.

Example 8: Substances Other than 1-Alkyl Alcohols as Modulators forUnmasking

As described herein above, 1-alkyl alcohols (used as reconfiguringmodulators) have been found to promote the formation of detectable LPSstructures. It was therefore desired to investigate whether other typesof substances than 1-alkyl alcohols might also have the ability topromote similarly detectable forms of LPS. This example shows theresults of a screening for substances other than 1-alkyl-alcohols whichmight be able to support formation of detectable LPS structures.

Materials and Methods

LPS (E. coli O55:B5, Sigma) 100 EU/ml was masked in polysorbate20/citrate for 24 hours at room temperature. Unmasking was initiated bysequential addition of 1 part stock solutions of CaCl₂(at 1 M), BSA (at100 mg/mL), SDS (at 1%) and substance X into 10 parts of a solution ofmasked LPS, wherein “substance X” represented the substance other than a1-alkyl alcohol, the ability of which as a reconfiguring modulator wasto be tested. Substance X was titrated in different concentrations.After unmasking, samples were diluted 1:10 and 1:100 in endotoxin-freewater and analyzed for detectable endotoxin using the EndoLISA® kit(Hyglos GmbH).

Results

Table 9 (below) shows the maximum LPS recoveries after unmasking asdependent on the substance used as modulator. Furthermore, suitableconcentrations of stock solutions of the respective substances forunmasking are shown.

TABLE 9 Optimum stock % LPS concentration of Substances recoverysubstance X sodium octyl sulfate (SOS) 20  30 mM 1-decanoic acid 57 100mM

As can be seen from the above, 1-alkyl alcohols are not the only classof compounds which may function as a reconfiguring modulator to promotethe formation of a detectable form of LPS. Other substances containinghigher oxidation states of oxygen (e.g. as in 1-decanoic acid) as wellas other heteroatoms than oxygen (e.g. as in sodium octyl sulfate (SOS))may also enable moderate to good unmasking.

The results indicate that substances which are similar in structure to1-alkylalcohols are also able to support unmasking to a certain extent.It appears that OH-derivatives of alkanes, preferably C₈-C₁₆ alkanes,preferably C₈-C₁₂ alkanes, preferably C₁₂ alkanes serve best to renderLPS susceptible to detection by Factor C-based assays.

Example 9: Unmasking Using Albumins from Different Sources and1-Dodecanol

As part of the verification of the improvement in unmasking by theaddition of bovine serum albumin (BSA) in masked samples containingpolysorbate 80, albumins from different sources were tested.

Materials and Methods

Masked samples (1 ml) containing 50 EU/ml of LPS (O55:B5) in polysorbate80/citrate buffer were unmasked by the addition of 100 μl of stocksolutions with different concentrations of albumins (bovine serumalbumin (BSA), very low endotoxin, Serva GmbH; human serum albumin (HSA,recombinantly produced in Pichia pastoris (Sigma Aldrich); and Ovalbumin(Ova), EndoGrade Ovalbumin, Hyglos GmbH) and subsequent addition of 100μl of a 100 mM 1-dodecanol stock solution). Concentrations of albuminstock solutions were 100, 33, 10, 3.3 and 1 mg/ml. Due to the lowersolubility of ovalbumin in water, a 100 mg/ml solution of ovalbumin wasnot prepared.

LPS recoveries were calculated following determination of detectable LPScontent using the EndoLISA® kit (Hyglos GmbH). For EndoLISA®measurements the unmasked samples were 1:10 and 1:100 diluted inendotoxin-free water and subsequently measured according to the kitinstructions.

Results

Table 10 (below) shows the unmasking efficiency from a polysorbate80/citrate masking system, as dependent on albumins from differentsources.

TABLE 10 [stock solution] protein (mg/ml) % LPS recovery BSA 100 66.0 3346.2 10 38.1 3.3 28.2 1 30.9 HSA 100 42.3 33 94.5 10 151.6  3.3 40.4 134.3 ovalbumin — nd 33 79.4 10 59.0 3.3 33.0 1 19.6 nd = no data

The data show that all albumins tested are able to support unmaskingfrom a polysorbate 80 masking system. Suitable final concentrations inthe unmasked samples are 10 mg/ml for BSA, 1 mg/ml for HSA and 3.3 mg/mlfor ovalbumin. The differences in optimum concentrations may result fromdifferent affinities of the albumins to the detergent in the maskedsample.

Example 10: The Effect of Various Chaotropic Salts on UnmaskingEfficiency

Unmasking using the combination of substances CaCl₂ (agent influencinghydrogen bonding), BSA (adsorbing modulator), SDS (displacing modulator)and 1-dodecanol (reconfiguring modulator) (this entire combination isreferred to as “CBSD”) has been shown above to efficiently unmask LPSwhen masked by e.g. TRITON™ (non-ionic surfactant) X-100. The presentexperiments investigate the effect of the nature of the chaotropic salt(agent influencing hydrogen bonding stability) on unmasking efficiency.To this end, the following experiments employ salts of increasingchaotropic properties: Na+, Mg²⁺ and Ca²⁺, in each case presented as thecorresponding chloride salt.

Materials and Methods

Endotoxin masking was performed as follows: 50 EU/ml of E. coli LPSO55:B5 was masked by allowing it to incubate for 3 days at roomtemperature in a 10 mM citrate buffer solution (pH 7.5) containing 0.05%TRITON™ (non-ionic surfactant) X-100. Here, TRITON™ (non-ionicsurfactant) X-100 functioned as the detergent masker.

Unmasking of endotoxin was performed as follows: 300, 100, 30, 10, 3 and1 μl of either a 5 M sodium chloride (NaCl), 1 M magnesium chloride(MgCl₂) or 1 M calcium chloride (CaCl₂) stock solution were added to 1ml aliquots of the masked samples and mixed. Subsequently, 100 μl of theother modulator components (BSA (adsorbing modulator), SDS (disruptingand displacing modulator) and 1-dodecanol (reconfiguring modulator))were added as described in Examples 1-5.

Results

Table 11 (below) shows the percentage of endotoxin recovery as dependenton each chaotropic salt and the most suitable final concentration ofeach salt in the unmasked sample.

TABLE 11 LPS recovery Concentration salt % (mM) NaCl 96.7 357 MgCl₂139.8 188 CaCl₂ 142.5 72

The data show that all the salts tested were able to support efficientunmasking of LPS from the masking detergent TRITON™ (non-ionicsurfactant) X-100 in combination with a multicomponent modulator systemincluding BSA (as adsorbing modulator), SDS (here, as disruptingmodulator) and 1-dodecanol (as disrupting and reconfiguring modulator).Furthermore, as described herein above, the amount of the salt requiredto achieve a comparable degree of unmasking efficiency decreased withincreasing chaotropic properties. These results allow several generalconclusions to be drawn. First, when using a salt to destabilize amasked complex between endotoxin and endotoxin masker, the chaotropiccharacter of this salt is an important factor in achieving efficientunmasking. Second, the amount of salt required to achieve efficientunmasking will generally vary inversely with the chaotropic strength ofthe salt employed.

Example 11: Unmasking of Endotoxin from Samples Containing Detergent andPhosphate Buffer

Most formulations of drugs which contain a protein (e.g. antibody) as anactive pharmaceutical ingredient (API) contain either non-ionicdetergents like polysorbate 20 or 80 together buffered in either citrateor phosphate. In such formulations, the detergent concentration isusually above the respective detergent's critical micellar concentration(CMC). Furthermore pH-values of such formulattions are often adjusted inorder to ensure optimum stability of the API.

With the above in mind, the investigations set out in this Examplesought to investigate the influence of pH value on unmasking efficiency.In order to approximate the conditions prevailing in pharmaceuticalformulations containing a protein API as closely as possible, thedetergents polysorbate 20 and polysorbate 80 were used as endotoxinmaskers, and the solutions were phosphate-buffered. In view of theresults described herein above, unmasking was performed using acombination of CaCl₂ (chaotropic salt as an agent which influenceshydrogen bonding stability), BSA (adsorbing modulator), SDS (here, asdisrupting modulator) and 1-dodecanol (disrupting and reconfiguringmodulator). As Ca²⁺ and PO₄ ³⁻ form non-soluble calcium-phosphatecomplexes, the calcium chloride solution was stabilized by addition of atwo-fold molar excess of citrate, pH 7.5.

Materials and Methods

Masking of endotoxin was performed as follows: To 1 ml samples, eachcontaining 10 mM of phosphate buffer of various pH-values and either0.05% polysorbate 20 or polysorbate 80, were added 100 EU/ml of E. coliLPS O55:B5. Masking was allowed to proceed by incubating these solutionsfor 7 days at room temperature. LPS-containing control samples ofphosphate buffers lacking detergent were prepared, incubated andmeasured in parallel to the masking samples.

Unmasking of endotoxin was performed as follows: A combination of CaCl₂,BSA, SDS and 1-dodecanol was added to each of the samples as describedin previous examples. To avoid calcium phosphate precipitation and toadjust the pH of the samples, a two-fold molar excess of citrate bufferpH 7.5 was added to each sample before addition of the unmaskingcomponents.

Endotoxin content of the masked samples was determined using theEndoZyme® kit of Hyglos GmbH at time zero, and after 7 days. Endotoxincontent of the unmasked samples was analyzed using the EndoLISA® kit ofHyglos GmbH. The percentage of LPS recovery after 7 days of masking andafter unmasking was calculated in reference to control samples at timezero.

Results

Table 12 (below) and FIGS. 10 and 11 show the percentage of LPS recoveryafter 7 days of masking as dependent on the pH-value and the percentageof LPS recovery after unmasking of the masked samples.

TABLE 12 Polysorbate 20 masker Polysorbate 80 masker phosphate recoveryrecovery recovery recovery buffer after after after after (pH-value)masking [%] unmasking [%] masking [%] unmasking [%] 1.6 81 143 104 1882.8 146 150 179 189 4.0 156 305 130 206 5.8 4 158 27 237 7.0 1 160 0 2218.9 0 156 0 187 12.1 3 192 1 128

The data show that masking in phosphate buffer solutions containingdetergent is strongly pH dependent. At pH values below 4, no maskingoccurs after one week of sample incubation. At pH values above 4 astrong masking effect is seen, resulting in detectable LPS recoveriesless than 1%.

The data also show conclusively that the unmasking approach implementedrenders the previously masked, undetectable LPS detectable. Independentof the pH-value and the extent of masking, 100% or more of LPS can berecovered, i.e. detected.

Example 12: Unmasking Using Other Displacing Modulators than SDS

As shown in the examples above, a combination ofCaCl₂/BSA/SDS/1-doedecanol efficiently unmasked endotoxin which ismasked by TRITON™ (non-ionic surfactant) X-100 detergent. Several of theexperiments described above suggests the importance of including SDS inthis scheme to achieve efficient unmasking. The aim of the experimentsdescribed in the present example is to investigate whether the modulatorcomponent SDS (here, as disrupting modulator) can be exchanged foranother detergent without negatively impacting the unmasking effectobserved using SDS.

Materials and Methods

Masking of endotoxin was performed as follows: 1 ml aliquots of 10 mMcitrate pH 7.5 containing 0.05% TRITON™ (non-ionic surfactant) X-100were prepared in endotoxin-free glass test tubes. Subsequently, 10 μl ofa 10,000 EU/ml stock solution of LPS (LPS 055 B5, Sigma L2637-5MG) wereadded, vortexed for 1 min and stored at room temperature for at least 24hours. A positive LPS control in water was prepared as follows: 10 μl ofa 10,000 EU/ml LPS stock solution was added to 1 ml of endotoxin-freewater, mixed and identically incubated as the masking preparations.Further details regarding the positive LPS-water control are indicatedin Example 1.

Unmasking of endotoxin was performed as follows: To masked solutions ofLPS, prepared as indicated above, CaCl₂, BSA, detergent X and1-dodecanol were added as described in the previous examples, where“detergent X” (disrupting modulator) was varied in identity andconcentration. The following detergents were tested: dioctylsulfosuccinate sodium salt (AOT), sodium dodecyl benzene sulfonate(SDBS), polyethylene glycol 4-nonylphenyl-3-sulfopropyl ether potassiumsalt (PENS) and p-xylene-2-sulfonic acid hydrate (XSA). Unmasking wasperformed as described in above examples, endotoxin content wasdetermined using the EndoLISA® kit of Hyglos GmbH, and the percentage ofLPS recovery was calculated with reference to the LPS-water positivecontrol. Further details regarding the LPS-water positive control aredescribed in Example 1 above.

Results

Table 13 shows the percentage of LPS recovery after unmasking usingdetergents other than SDS in the CaCl₂/BSA/[detergent X]/1-dodecanolunmasking approach.

TABLE 13 Concentration LPS recovery Detergent optimum [%] AOT 0.01% 24SDBS 0.01% 34 PENS 0.10% 23 XSA 0.05% 26

The data show that other detergents besides SDS are able to supportunmasking as a disrupting modulator in a CaCl₂/BSA/[detergentX]/1-dodecanol unmasking approach. Furthermore, in the absence of1-dodecanol no detergent was able to unmask LPS from TRITON™ (non-ionicsurfactant) X-100. As mentioned above, this suggests that 1-dodecanolmay play an important role (at least) as a reconfiguring modulator whichmay be crucial for mediating the transition of endotoxin from asolubilized (undetectable) to an aggregated (detectable) state.

Example 13: Unmasking from Buffered Antibody Compositions as Dependenton the Masking Detergent

The most commonly used formulations of protein-based drug productscontain phosphate buffer and non-ionic detergents such as polysorbate 20or polysorbate 80. Further, antibodies constitute one of the mostcommonly formulated pharmaceutical protein products. With this in mind,we sought to confirm whether the above unmasking approaches fordetergents- or protein-masking systems are suitable for unmaskingendotoxin in systems containing both detergent and protein, where theprotein is an antibody buffered in phosphate. Polysorbate 20 and 80 werechosen as masking detergents in these experiments because these twodetergents are the most commonly used detergents in protein drugformulations.

Materials and Methods

Endotoxin masking was performed as follows: 50 EU/ml of endotoxin (E.coli O55:B5; Sigma L2637-5MG) was added to 1 ml aliquots of an antibodysolution containing 10 mg/ml of a bovine polyclonal IgG antibodypreparation, dissolved in 10 mM sodium phosphate pH 7.5 and 50 mM NaCl.Subsequently, either polysorbate 20 or polysorbate 80 were added to afinal concentration of 0.05%, and the solutions were incubated for 3days at room temperature to allow masking to occur. Further, controlscontaining the buffer solution without detergent or antibody, as well asthe buffer solution containing either the antibody or the respectivepolysorbate were prepared and treated like the masking samples. Each ofthe controls contained the same amount of LPS.

Unmasking was performed as follows: Unmasking was performed by additionof either 1-dodecanol or BSA/1-dodecanol or CaCl₂/BSA/SDS/1-dodecanol.100 μl of the following stock solutions were added to 1 ml of samplesolution: CaCl₂ (1 M), BSA (100 mg/ml), SDS (1%) and 1-dodecanol (100,10 or 1 mM). Furthermore, before addition of calcium chloride to asample, the sample was stabilized against calcium phosphateprecipitation by the addition of a final concentration of 200 mM sodiumcitrate pH 7.5. All stock solutions were added sequentially withtwo-minute mixing steps following each addition. After addition andmixing of the last component the samples were incubated for at least 30minutes at room temperature. Afterwards, the samples were diluted 1:10and 1:100 in endotoxin-free water and analyzed for endotoxin contentusing the EndoLISA kit (Hyglos GmbH). The percentage of LPS recovery wascalculated with reference to the determined endotoxin content in thebuffer control (discussed in more detail in Example 1).

Results

Table 14a (below) shows the percentage of LPS recovery of the watercontrol, the buffer without detergent, the buffer containing antibody ordetergent and the buffer containing antibody and detergent after 3 daysof incubation at room temperature.

TABLE 14a polysorbate polysorbate 20 80 LPS re- LPS re- sample typeingredients covery (%) covery (%) water control water 100 100 bufferbuffer without detergent 102 99 masking control buffer + antibody 31 44masking control buffer + polysorbate 0 2 masking control buffer +polysorbate + 0 9 antibody

Table 14b (below) shows the percentage of LPS recovery from an antibodysolution after unmasking containing either polysorbate 20 or 80.Furthermore, it shows the concentrations of the added stock solutions.

TABLE 14b polysorbate polysorbate 20 80 [CaCl2] [BSA] [SDS][1-Dodecanol] LPS re- LPS re- (M) (mg/ml) (%) (mM) covery (%) covery (%)— — — 100 16.6 9.1 — — — 10 19.9 6.8 — — — 1 0.0 5.0 — 100 — 100 40.811.2 — 100 — 10 2.6 6.3 — 100 — 1 1.6 11.5 1 100 1 100 4.8 3.0 1 100 110 15.9 23.1 1 100 1 1 67.3 90.8

The data show that the buffer solutions without polysorbate 20 or 80 donot mask the added LPS. The buffer solutions containing antibody but nopolysorbate mask ˜55% to 70% of the LPS, suggesting that the antibodyprotein contributes a masking effect of its own. The LPS recoveries frombuffer solutions containing polysorbate or polysorbate and antibody arebelow 10% when no unmasking measures are taken. Thus, not only thedetergent but also the antibody is responsible for masking of LPS.

LPS recoveries after unmasking from the masking complexes containingLPS, detergent and antibody are low using 1-dodecanol alone (9 and 17%for polysorbate 80 and 20, respectively). Using a combination of BSA(adsorbing modulator) and 1-dodecanol (disrupting and reconfiguringmodulator) allowed moderate LPS recoveries of 11 and 41% for polysorbate80 and 20, respectively. Unmasking using a combination of CaCl₂, BSA(adsorbing modulator), SDS (displacing modulator) and 1-dodecanol(disrupting and reconfiguring modulator), results in recoveries of 67%and 91% of the masked LPS for polysorbate 20 and 80, respectively.Interestingly, unmasking was achieved using a 1-dodecanol stock solutionwith a concentration as low as 1 mM. Furthermore, in contrast to theunmasking from detergent systems lacking protein, using 1-dodecanol(disrupting and reconfiguring modulator) or BSA (adsorbing modulator)and 1-dodecanol (disrupting and reconfiguring modulator) do not unmaskwith greater efficiency than 50%. As shown for lysozyme above, efficientunmasking was only be achieved in the presence of CaCl₂, BSA, SDS and1-dodecanol.

Example 14: Unmasking from Compositions Containing Antibody andPolysorbate 20 as Dependent on the Buffer Substance

It was determined in above Example 14 that the inventive unmaskingapproaches described herein are suitable for unmasking compositionswhich contain both detergent and buffered protein (antibody). In view ofthis, it was then desired to investigate the influence of buffer onunmasking efficiency. To this end, we chose 10 mM citrate or 10 mMphosphate buffer of pH 7.5, because these are the most commonly usedbuffers in protein drug formulations.

Materials and Methods

Endotoxin masking was performed as follows: 50 EU/ml of endotoxin (E.coli O55:B5; Sigma L2637-5MG) were added to 1 ml aliquots of an antibodysolution containing 10 mg/ml of a bovine polyclonal IgG antibodypreparation, dissolved in either 10 mM sodium phosphate containing 50 mMsodium chloride or 10 mM sodium citrate pH 7.5 containing 150 mM sodiumchloride. Subsequently, polysorbate 20 was added to a finalconcentration of 0.05% and samples were masked for 3 days at roomtemperature. Further, positive controls containing the buffer solutionwithout detergent or antibody, as well as the buffer solution containingeither the antibody or the respective polysorbate were prepared andtreated like the masking samples. Each of the positive controlscontained the same amount of LPS.

Endotoxin unmasking was performed as follows: Unmasking was performed byaddition of either 1-dodecanol or a combination of BSA (adsorbingmodulator) and 1-dodecanol (disrupting and reconfiguring modulator) orCaCl₂, BSA (adsorbing modulator), SDS (displacing modulator) and1-dodecanol (disrupting and reconfiguring modulator). 100 μl of each ofthe following stock solutions were sequentially added to 1 ml of samplesolution: CaCl₂ (1M), BSA (10 mg/ml), SDS (1%) and 1-dodecanol (100, 10or 1 mM). Furthermore, before addition of calcium chloride to aphosphate buffer-containing sample, this sample was stabilized againstcalcium phosphate precipitation by the addition of a final concentrationof 200 mM sodium citrate pH 7.5. All stock solutions were addedsequentially with two-minute mixing steps after each addition. Afteraddition and mixing of the last component the samples were incubated forat least 30 minutes at room temperature. Afterwards, the samples werediluted 1:10 and 1:100 in endotoxin-free water and analyzed forendotoxin content using the EndoLISA kit (Hyglos GmbH). The percentageof LPS recovery was calculated with reference to the determinedendotoxin content in the positive control (discussed in more detail inExample 1).

Results

Table 15 (below) shows the percentage of LPS recovery from an antibodysolution after masking and unmasking containing either citrate orphosphate as buffer substance.

TABLE 15 citrate phosphate buffer buffer LPS LPS sample type ingredientrecovery (%) recovery (%) water control water 100 100 masking controlbuffer + antibody 40 31 masking control buffer + polysorbate 20 0 0masking control buffer + polysorbate 20 + 1 0 antibody LPS [1- LPS [1-unmasking re- dodec- re- dodec- sample approach/ covery anol] coveryanol] type ingredients (%) (mM) (%) (mM) unmasked 1-dodecanol 26 100 17100 sample * unmasked BSA/ 49 100 41 100 sample * 1-dodecanol unmaskedCaCl₂/ 87 100 67 1 sample * BSA/SDS/ 1-dodecanol * “Unmasked” samplescontained antibody.

The data show that the buffer solutions containing antibody but nopolysorbate, mask 60 to 70% of the LPS (based on the recovery of 40% andabout 30% LPS for citrate and phosphate buffers, respectively). The LPSrecoveries from buffer solutions containing polysorbate or polysorbateand antibody are below 1%. In these cases, masking is independent of thebuffer present.

LPS recoveries after unmasking from the compositions containing LPS,detergent and antibody are low using 1-dodecanol alone (17% and 26% forphosphate and citrate, respectively) and moderate using a combination ofBSA (adsorbing modulator) and 1-dodecanol (disrupting and reconfiguringmodulator) (41% and 49% for phosphate and citrate, respectively).Unmasking using a combination of CaCl₂, BSA (adsorbing modulator), SDS(displacing modulator and 1-dodecanol (disrupting and reconfiguringmodulator) results in recoveries of 67% and 87% of the masked LPS forphosphate and citrate, respectively. Interestingly, the necessaryconcentration of 1-dodecanol stock solution for efficient unmaskingdiffers strongly between the buffer systems used (100 mM forantibody/detergent/citrate and 1 mM for antibody/detergent/phosphate).The data clearly show that efficient unmasking of endotoxin incompositions comprising both protein (antibody) and detergent can beachieved by adjustment of 1-dodecanol concentration.

Example 15: Masking and Unmasking of an Antibody Solution Containing LPSfrom Unknown Source

To show that unmasking is not only possible from solutions containingLPS from a known source, we tested a commercially available mousemonoclonal antibody for diagnostic use which contains an LPScontamination, where the source of the LPS is unknown. Furthermore, thisantibody was dissolved in a buffer composition which corresponds to theformulation of the known antibody drug product Rituximab (MabThera®,Rituxan®).

Materials and Methods

Determination of endotoxin contamination: A mouse monoclonal antibody(MAB 33, Roche Diagnostics) was dissolved in a solution containingcitrate and sodium chloride of pH 6.5 and stored at 4° C. The finalconcentrations of citrate, sodium chloride and antibody were 25 mM, 150mM and 10 mg/ml, respectively. Directly after solubilization of theantibody, the endotoxin content was analyzed using EndoZyme® andEndoLISA® detection kits (Hyglos GmbH). The determined endotoxin contentwas 11 EU/mg of antibody.

LPS masking was initiated by addition of polysorbate 80 to a finalconcentration of 0.07% and increasing the temperature to ambientconditions (22° C.). Afterwards, 1 ml aliquots of the samples wereincubated at room temperature for 3 days to allow the endottoxin presentto become masked.

Unmasking was performed as follows: Unmasking was performed by additionof either 1-dodecanol (disrupting and reconfiguring modulator); or acombination of BSA (adsorbing modulator) and 1-dodecanol (disrupting andreconfiguring modulator); or a combination of CaCl₂, BSA (adsorbingmodulator), SDS (displacing modulator) and 1-dodecanol (disrupting andreconfiguring modulator). 100 μl of each of the following stocksolutions were sequentially added to 1 ml of sample solution: CaCl₂ (1M), BSA (10 mg/ml), SDS (1%) and 1-dodecanol (100, 10 or 1 mM). Allstock solutions were added sequentially with two-minute mixing stepsafter each addition. After addition and mixing of the last component thesamples were incubated for at least 30 minutes at room temperature.

Afterwards, the samples were diluted 1:10 and 1:100 in endotoxin freewater and analyzed for endotoxin content using EndoLISA® (Hyglos GmbH).The percentage of LPS recovery was calculated in reference to thedetermined endotoxin content at time zero.

Results

Table 16 (below) shows the percentage of endotoxin recovery as dependenton the masking time, the presence or absence of polysorbate 80 andunmasking from antibody/polysorbate 80 solution.

TABLE 16 LPS recovery sample type ingredients (%) control t(0) buffer +antibody 100 masking control (3 days) buffer + antibody 57 maskingcontrol (3 days) buffer + polysorbate 80 0 masking control (3 days)buffer + polysorbate 80 + 3 antibody LPS [1- unmasking approach/recovery dodecanol] sample type ingredients (%) (mM) unmasked sample *1-dodecanol 45 100 unmasked sample * BSA/1-dodecanol 68 100 * “Unmasked”samples contained antibody.

The data show that the buffer solution containing antibody but nopolysorbate masks 40% of the LPS within 3 days of incubation at roomtemperature. However, incubation in buffer containing either polysorbate80 or antibody and polysorbate 80, results in endotoxin recoveriessmaller than 4%.

Unmasking from the antibody/detergent samples results in recoveries of45% using 1-dodecanol (disrupting and reconfiguring modulator); 68%using a combination of BSA (adsorbing modulator) and 1-dodecanol(disrupting and reconfiguring modulator); and 179% using a combinationof CaCl₂, BSA (adsorbing modulator), SDS (displacing modulator) and1-dodecanol (disrupting and reconfiguring modulator). In the lattercase, the best recovery is achieved using a 1 mM 1-dodecanol stocksolution.

The experiments described in this example show that, when present,naturally occurring endotoxin (NOE) can be detected by a suitableendotoxin detection system. Furthermore, these experiments show thatsuch NOE can be masked in the manner described herein above, i.e. thedanger of masking applies not only for purified endotoxin, but also forNOE. The ability of the inventive methods as described herein to unmasksuch NOE further demonstrate their applicability to situations in whichNOE has been masked, proving their effectiveness of the inventivemethods to unmask masked NOE. These findings are relevant to theconditions prevailing in industry, where production processes oftenstart with an expressed protein in the presence of NOE, and the latteris masked by incorporation of detergent to prevent unwanted proteinaggregation. Overall, then, the results of the experiments described inthis example demonstrate that the inventive methods are able to unmaskendotoxin under conditions of relevance for the pharmaceutical industry.

These data also clearly show that unmasking is independent of the sourceand purity of the LPS.

In all three cases of masking in antibody solutions (Examples 13, 14 and15), it can be seen that masking is not only due to the detergentcomponent in the composition but also to some extent to the antibodyitself. The most efficient unmasking approach is to use a combination ofCaCl₂, BSA (adsorbing modulator), SDS (displacing modulator) and1-dodecanol (disrupting and reconfiguring modulator) to unmask theendotoxin. Here, analogies can be seen to the lysozyme case (discussedin Example 7 above), in which the protein itself plays a role as anendotoxin masker. Interestingly, in all cases, the concentration of1-dodecanol should be optimized for efficient unmasking.

Example 16: General Evaluation of Unmasking Approach as Applied to a NewComposition in Question

As shown in the above examples, the choice of the approach taken tounmask endotoxin suspected of being present, but masked in a compositionwill depend on a number of factors. For instance, as the foregoingexamples have shown, it is sometimes possible to achieve efficientunmasking using a single-component modulator which doubles as adisrupting modulator and a reconfiguring modulator, as defined hereinabove. On the other hand, in some instances, the modulator should be amodulator system with two or more components, for instance a displacingmodulator and/or an adsorbing modulator, depending on what measures areneeded to destabilize and disrupt the endotoxin/endotoxin masker complexsufficiently such that the endotoxin is liberated and can be mediatedinto an aggregated form which can be detected.

The above examples start from known, controlled solution conditions inorder to illustrate concepts underlying the present invention. In areal-world scenario, however, in which the methods of the invention areto be applied to a new composition in question, it is necessary to firstevaluate the approach of the methods of the invention before meaningfulresults can be obtained. The present example addresses such avalidation, setting out a generic scheme by which the methods of theinvention may be calibrated to a new composition in question. To thisend, an iterative unmasking approach is necessary, starting with aninitial screening for the best suited unmasking approach followed bysubsequent improvement steps for adjustment of optimum unmaskingcomponent concentrations.

General Description of an Evaluation Process for a Given Composition

Generally, FIG. 12 shows a scheme which schematically sets out the stepswhich one would normally take in evaluating the inventive methods for anew, unknown composition.

As will be clear from the above, ultimate detection of initially maskedendotoxin depends on the ability to convert this endotoxin from stablybound (masked) form to an aggregated from which is unmasked andtherefore detectable. The component of the modulator responsible forthis final conversion is the reconfiguring modulator. The first step ofFIG. 12 reflects this, in that it specifies a first step of determiningan optimal concentration of reconfiguring modulator (e.g. 1-dodecanol).Step 2 then optimizes the concentration of adsorbing modulator, if thismodulator is included. Step 3 then optimizes the concentration ofdisplacing modulator, if this modulator is included.

It should be emphasized that not all three steps will always be needed.If one already sees that a composition, for example a pharmaceuticalcomposition, in question contains significant amounts of endotoxinfollowing step one, then this answer may already be enough to concludethat the composition thought to be endotoxin-free was really not.

Specific Description of Evaluation Process for a Given Composition

FIG. 13 shows the combinations and concentrations of stock solutions forselecting and optimizing the unmasking process. The unmasking approachesare divided into different possible scenarios A, B and C, depending onwhich substance or combination of substances is/are used in unmasking.Unmasking approach A describes an unmasking approach in which only1-dodecanol is used as a modulator. Unmasking approach B describes anunmasking approach in which the modulator system is composed of1-dodecanol and BSA. Unmasking approach C describes an unmaskingapproach in which the modulator system is composed of 1-dodecanol, BSAand SDS, and is performed in the presence of CaCl₂.

Procedure

Add 100 μl of the unmasking component stock solutions to 1 ml of maskedsample. After addition of one component, mix sample thoroughly byvortexing for 2 minutes. Then, add the next component and mix. Afteraddition of all components and subsequent mixing, incubate samplesfor >30 minutes at room temperature. Afterwards, analyze samples forendotoxin content using an appropriate endotoxin testing method, e.g.the EndoLISA® kit of Hyglos GmbH.

Example 17: Detection of Unmasked Endotoxin Using a Recombinant Factor CAssay

This experiment investigates the effect of unmasking endotoxin using amulti-component modulator comprising CaCl₂, BSA, SDS and dodecanol.Endotoxin content of the masked and unmasked samples was determinedusing the EndoZyme® kit of Hyglos GmbH. The experiment was performed inorder to show that detection of unmasked endotoxin can be achieved usingdifferent detection assays.

Materials and Methods

Endotoxin (E. coli O55:B5, Sigma L2637-5MG) was masked in solutionscontaining 1×PBS-buffered 0.05 wt % Polysorbate 80 or 1×PBS buffered0.05 wt % Polysorbate 20 for 3 days at room temperature.

Unmasking was performed as follows: Unmasking was performed by acombination of sodium citrate, CaCl₂, BSA, SDS and 1-dodecanol. 150 μLof sodium citrate and 100 μl of each of the following stock solutionswere added to 1 ml of sample solution: sodium citrate (1.375 M pH 7.5),CaCl₂ (1 M), BSA (10 mg/ml), SDS (1%) and 1-dodecanol (1 mM).1-dodecanol was solubilized in 70% EtOH. In a separate masking control,no unmasking was performed.

All stock solutions were added sequentially with two-minute mixing stepsafter each addition. After addition and mixing of the last component thesamples were incubated for at least 30 minutes at room temperature.

Subsequently, masked (masking control) and unmasked samples were dilutedstepwise 1:10 and 1:5 in depyrogenated water (final dilution 1:50). Arecombinant Factor C assay (EndoZyme®) was used for detection ofendotoxin.

Results

Table 17 (below) shows the percent recovery, measured using arecombinant Factor C assay (EndoZyme®), of endotoxin recovered from thetwo masking systems specified above in this example.

TABLE 17 Detection of unmasked endotoxin using recombinant Factor CRecombinant Factor C PBS + P80 PBS + P20 Sample [EU/mL] [EU/mL] Positivecontrol 9.3 6.8 Recovery [%] Recovery [%] Masking control 0 0 Afterunmasking 65 66

The masking control showed no endotoxin recovery in either sample.Unmasking of endotoxin in polysorbate 80 or polysorbate 20 resulted inendotoxin recovery of 65% and 66%, respectively, with reference to thepositive control (endotoxin content in depyrogenated water). The resultsindicate the efficient demasking of endotoxin using a multi-componentmodulator comprising Sodium citrate, CaCl₂, BSA, SDS and dodecanol asdetected by a recombinant Factor C detection system (EndoZyme®). Thisexperiment proves that the detection of unmasked endotoxin isindependent of the endotoxin detection system used.

Accordingly, unmasked endotoxin may be detected using the endotoxindetection system employed in previous examples, but may also be detectedusing an endotoxin detection system differing from that used in previousexamples.

Example 18: Detection of Unmasked Endotoxin Using a Limulus AmeboecyteLysate (LAL) Assay

This experiment investigates the detection of unmasked endotoxin using adetection assay different from the recombinant Factor C assay(EndoZyme®), i.e. the Limulus Ameboecyte Lysate (LAL) assay. Theexperiment was performed in order to further corroborate that detectionof endoxin unmasking does not depend on the detection assay.

Materials and Methods

Endotoxin (E. coli O55:B5, Sigma L2637-5MG). was masked in solutionscontaining 1×PBS-buffered 0.05 wt % Polysorbate 80 or 1×PBS buffered0.05 wt % Polysorbate 20 for 3 days at room temperature.

Unmasking was performed as follows: Unmasking was performed by acombination of sodium citrate, CaCl₂, BSA, SDS and 1-dodecanol. 150 μLof sodium citrate and 100 μl of each of the following stock solutionswere added to 1 ml of sample solution: sodium citrate (1.375 M pH 7.5),CaCl₂ (1 M), BSA (10 mg/ml), SDS (1%) and 1-dodecanol (1 mM).1-dodecanol was solubilized in 70% EtOH.

All stock solutions were added sequentially with two-minute mixing stepsafter each addition. After addition and mixing of the last component thesamples were incubated for at least 30 minutes at room temperature.

Subsequently, masked (masking control) and unmasked samples were dilutedstepwise 1:10 and 1:5 in depyrogenated water (final dilution 1:50). Akinetic LAL-based chromogenic assay (kinetic-QCL®, Lonza) was used fordetection of endotoxin. Masking control reflects the detectableendotoxin content without unmasking. In a separate masking control, nounmasking was performed.

Results

Table 18 (below) shows the percent recovery, measured using an LAL assay(kinetic QCL®, Lonza), of endotoxin recovered from the two maskingsystems specified above in this example.

TABLE 18 Unmasking using an LAL assay LAL PBS + P80 PBS + P20 Sample[EU/mL] [EU/mL] Positive control 11.6 7.2 Recovery [%] Recovery [%]Masking control 3 0 After unmasking 96 47

The masking control showed no endotoxin recovery in both samples.Unmasking of endotoxin in polysorbate 80 or polysorbate 20 resulted inendotoxin recovery of 96% and 47%, respectively, with reference to thepositive control (endotoxin content in depyrogenated water). The dataclearly demonstrate that unmasking of endotoxin can be detected with theLAL detection assay and that detection of endotoxin unmasking does notdepend on the detection assay.

Example 19: Variation of Alkanols (Aliphatic Alcohols) as Modulators forUnmasking Using a Multi-Component Modulator

This experiment investigates unmasking of different endotoxins usingdifferent alkanols. The experiment was performed in order to investigatethe unmasking efficiency of different alkanol compounds in themulti-component modulator.

Materials and Methods

Endotoxin from E. coli O55:B5 (Sigma L2637-5MG), S. abortus equi (Acila1220302) and K. pneumoniae (LMU) were masked in solutions containing 10mM sodium citrate and 0.05 wt % Polysorbate 20 for three days at roomtemperature.

Unmasking was performed as follows: Unmasking was performed by acombination of NaCitrate, CaCl₂, BSA, SDS and 1-dodecanol. 150 μL ofsodium citrate and 100 μl of each of the following stock solutions wereadded to 1 ml of sample solution: sodium citrate (1.375 M pH 7.5), CaCl₂(1 M), BSA (10 mg/ml), SDS (1%) and a certain concentration of1-dodecanol. The alkanols and alkanol mixtures used in themulti-component modulator systems were solubilized in EtOH;concentrations are listed in Table 19a (below). In a separate maskingcontrol, no unmasking was performed.

All stock solutions were added sequentially with two-minute mixing stepsafter each addition. After addition and mixing of the last component thesamples were incubated for at least 30 minutes at room temperature.

TABLE 19a Unmasking Concentration approach: Alkanols (size) [mM] 1Octanol (C8) 1.0 2 Decanol (C10) 1.0 3 Dodecanol (C12) 1.0 4Tetradecanol (C14) 1.0 5 Hexadecanol (C16) 1.0 6 Octanol (C8) 0.3Decanol (C10) 0.3 Dodecanol (C12) 0.3 7 Decanol (C10) 0.3 Dodecanol(C12) 0.3 Tetradecanol (C14) 0.3 8 Dodecanol (C12) 0.3 Tetradecanol(C14) 0.3 Hexadecanol (C16) 0.3

Afterwards, the samples were diluted 1:10 and 1:100 in endotoxin freewater and analyzed for endotoxin content using EndoLISA® (Hyglos GmbH).The percentage of LPS recovery was calculated in reference to thedetermined endotoxin content at time zero (summarized in Table 19b,below).

Results

Table 19b (below) shows the percent recovery after masking (maskingcontrol) and after unmasking using the EndoLISA® assay (Hyglos) from theabove masking system by various unmasking approaches employing differentalkanols (aliphatic alcohols) or alkanol mixtures (aliphatic alcoholmixtures) as specified above in Table 19a.

TABLE 19b Unmasking of different endotoxins using Ca, BSA, SDS andvarying alkanols, as detected by the EndoLISA ® assay Endotoxin K.pneumoniae * S. abortus equi E. coli O55:B5 [EU/mL] [EU/mL] [EU/mL]Positive Control 191 51 68 Recovery [%] Recovery [%] Recovery [%]Masking Control 0 0 0 Unmasking approach (alkanol size) 1 (C8) 75 0 2 2(C10) 52 0 0 3 (C12) 147 62 76 4 (C14) 94 108 71 5 (C16) 99 83 22 6 (C8,C10, C12) 60 14 6 7 (C10, C12, C14) 126 108 43 8 (C12, C14, C16) 126 17343 * For unmasking of K. pneumoniae 150 μL of CaCl₂ were added.

The above results indicate that unmasking of K. pneumoniae was achievedwith octanol (75% recovery), dodecanol (147%), tetradecanol (94%) andhexadecanol (99%), as well as with different combinations of alkanols(see e.g. unmasking approaches 7 and 8). Unmasking with decanol,however, was less efficient (52%). Unmasking of the S. abortus equi LPSwas most efficient using tetradecanol (108%), hexadecanol (82%),dodecanol (62%), or different combinations of alkanols. Effectiveunmasking of E. coli 055:65 was observed for dodecanol (76%) andtetradodecanol (71%). No endotoxin recovery was observed for the maskingcontrols.

These results indicate that the most efficient unmasking (independent ofthe nature of the endotoxin) was achieved using dodecanol ortetradecanol, or using combinations of dodecanol and tetradecanol with afurther alkanol (e.g. decanol in demasking 7). These results alsoindicate that all multi-component modulator systems with C₁₂, C₁₄ and/orC₁₆ aliphatic alcohols exhibited efficient unmasking of endotoxin.

The range of alkyl chain length of the fatty alcohols for efficientunmasking seems to depend on the endotoxin source. The differences inthe unmasking efficiencies may depend to a certain extent on theheterogeneity in length of the acyl chains of the β-hydroxy-fatty acidswhich are present in the Lipid A portion of endotoxin. Between andwithin bacterial species, these acyl chains can vary in length from C₁₀to C₂₈ (Endotoxin in health and disease, edited by H. Brade (1999), p98et seq: “Chemical structure of Lipid A: Recent advances in structuralanalysis of biologically active molecules”; Marcel Dekker Inc, NewYork). However, most commonly β-hydroxy-fatty acids with chains lengthof C14 and C16 are appended to the diglucosamine of Lipid A. Thus,unmasking is in all cases most efficient in the presence of fattyalcohols with alkyl chain length between C12 and C14, although unmaskingof endotoxin is also observed for other alkyl chain lengths in theC8-C16 range.

Example 20: Variation of Alkanols (Aliphatic Alcohols) as Modulators forUnmasking Using a Single-Component Modulator

This experiment was performed to investigate the effect of variousalkanols (aliphatic alcohols) on unmasking in the absence of additionalmodulator components. The experiment thus investigates the efficiency ofendotoxin unmasking using various alkanols (aliphatic alcohols) assingle-component modulators.

Materials and Methods

Endotoxin E. coli O55:B5 (Sigma L2637-5MG) was masked in solutionscontaining 10 mM sodium citrate and 0.05 wt % Polysorbate 20 for 3 daysat room temperature.

In order to unmask the samples, samples (1 mL) were mixed with 100 μL ofthe particular alkanol (i.e. aliphatic alcohol). The alkanols used inthe single-component modulator systems were solubilized in EtOH.Concentrations are shown in Table 20a (below).

TABLE 20a Variation of alkanols (aliphatic alcohols) Unmasking ApproachAlkanols (size) Concentration [mM] 1 Dodecanol (C12) 50 mM 2 Tridecanol(C13) 50 mM 3 Tetradecanol (C14) 50 mM

After addition of unmasking agents, the samples were incubated for 30minutes and diluted 1:10 as well as 1:100 in depyrogenated water.Endotoxin was detected in both dilutions and the stated recoveryreflects the mean recovery of both dilutions. The masking controlreflects the non-treated sample after masking, i.e. the solution is notunmasked. The EndoLISA® assay was used for endotoxin detection.

Results

Table 20b (below) shows the percent recovery, measured using theEndoLISA® assay (Hyglos), of endotoxin recovered from the above maskingsystem by various unmasking approaches employing different alkanols(aliphatic alcohols) in different unmasking approaches usingsingle-modulator systems as specified above in Table 20a.

TABLE 20b Unmasking using different alkanols (EndoLISA ®) E. coli O55:B5(gel) Endotoxin [EU/mL] Positive Control 111 Recovery [%] MaskingControl 0 Unmasking approach (alkanol size) 1 (C12) 56 2 (C13) 41 3(C14) 22.6

The results indicate that a single-component modulator consisting ofdodecanol (unmasking approach 1) was most efficient in unmasking of E.coli 055:65 (56% recovery), whereas single-component modulatorsconsisting of tridecanol (unmasking approach 2) or tetradecanol(unmasking approach 3) resulted in less recovery of E. coli 055:65 (41%and 22.6%, respectively). As expected, the masking controls showed noendotoxin recovery. In summary, the data demonstrate that the mostefficient alkanol (aliphatic alcohol) for unmasking of E. coli 055:65,when used as a single-component modulator system, is dodecanol, followedby tridecanol and tetradecanol.

1. An aqueous composition comprising a protein, an aliphatic compoundwith C8-C16 as the main chain, and lipopolysaccaride (LPS), wherein thealiphatic compound is an alkanol, and wherein the protein is chosen froman antibody, an antibody fragment, a hormone, an enzyme, a fusionprotein, a protein conjugate and any combination thereof.
 2. The aqueouscomposition according to claim 1, wherein the alkanol is an unbranched1-alkanol, preferably 1-dodecanol.
 3. The aqueous composition accordingto claim 1, wherein the alkanol is a branched compound with at least onesubstitution in the main chain selected from a methyl, ethyl, propyl andbutyl group.
 4. The aqueous composition according to claim 1, furthercomprising a detergent selected from an anionic detergent, a cationicdetergent, a nonionic detergent, an amphoteric detergent and anycombination thereof.
 5. The aqueous composition according to claim 4,wherein said detergent is an anionic detergent chosen from the groupconsisting of: alkyl sulfates, preferably ammonium lauryl sulfate orsodium lauryl sulfate (SDS); alkyl-ether sulfates, preferably sodiumlaureth sulfate or sodium myreth sulfate; cholesterol sulfate;sulfonates, preferably dodecylbenzensulfonate, sodiumlauryl sulfoacetateor xylene sulfonate; alkyl sulfo succinates, preferably disodium laurylsulfosuccinate; sulfoxides, preferably dodecyl methyl sulfoxide;phosphates, preferably trilaureth-4 phosphate; and carboxylates,preferably sodium stearate or sodium lauroyl sarcosinate.
 6. The aqueouscomposition according to claim 4, wherein said detergent is a cationicdetergent chosen from the group consisting of: primary amines; secondaryamines; tertiary amines; and quaternary ammonium cations such asalkyltrimethylammonium salts (preferably cetyl trimethylammonium bromide(CTAB), or cetyl trimethylammonium chloride (CTAC)); cetylpyridiniumchloride (CPC); quaternary ammonium detergents, preferablytris[2-(2-hydroxyethoxy)ethyl]-octadecyl-ammonium phosphate (Quaternium52); and hydroxyethylcellulose ethoxylate, quaternized(Polyquaternium-10).
 7. The aqueous composition according to claim 4,wherein said detergent is a nonionic detergent chosen from the groupconsisting of: polyoxyethylene glycol sorbitan alkyl esters(polysorbates), preferably polysorbate 20 (Tween-20), polysorbate 40,polysorbate 60 or polysorbate 80 (Tween-80); polyoxyethylene glycolalkyl ethers; polyoxypropylene glycol alkyl ethers; glucoside alkylethers; polyoxyethylene glycol octylphenol ethers; polyoxyethyleneglycol alkylphenol ethers; glycerol alkyl esters; sorbitan alkyl esters;block copolymers of polyethylene glycol and polypropylene glycol;cocamide MEA; sterols, preferably cholesterol; cyclodextrins;poloxamers, preferably Pluronic block polymers; and cocamide DEA.
 8. Theaqueous composition according to claim 4, wherein said detergent is anamphoteric detergent chosen from the group consisting of: CHAPS(3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate); sultaines,preferably cocamidopropyl hydroxysultaine; betaines, preferablycocamidopropyl betaine; amino oxides, preferably palmitamine oxide,laurylamine oxide and amine oxide of general formula R³N+O⁻, wherein R³is C₅-C₁₈ alkyl, C₅-C₁₈ alkenyl, or C₅-C₁₈ alkynyl; and lecithin.
 9. Theaqueous composition according to claim 4, wherein the detergent isselected from polysorbate 20 (Tween 20), Polysorbate 80 (Tween 80),Poloxamer 188 (Pluronic F68), Octoxynol 9 (Triton X-100),Laurylamineoxid, tris[2-(2-hydroxyethoxy)ethyl]-octadecyl-ammoniumphosphate (Quaternium 52), trilaureth-4 phosphate and sodium stearate.10. The aqueous composition according to claim 1, wherein the antibodyfragment is selected from a Fab, a Fab′, a F(ab′)2 and an Fv, a singlechain antibody and any combination thereof.
 11. The aqueous compositionaccording to claim 1, containing a further protein which is an albumin,preferably human serum albumin, bovine serum albumin and/or ovalbumin.12. The aqueous composition according to claim 1, further comprising achaotropic agent, a cation or a combination thereof.
 13. The aqueouscomposition according to claim 12, wherein the composition comprises achaotropic agent selected from urea, guanidinium chloride, butanol,ethanol, lithium perchlorate, lithium acetate, magnesium chloride,phenol, propanol and thiourea.
 14. The aqueous composition according toclaim 12, wherein the composition comprises a cation that is a divalentcation.
 15. The aqueous composition according to claim 14, wherein thedivalent cation is selected from Ca2+, Mg2+, Sr2+ and Zn2+.
 16. Theaqueous composition according to claim 11, wherein the further proteinis present in a concentration from 0.1-20 mg/ml, preferably from 1-10mg/ml, the aliphatic compound is present in the concentration from0.01-100 mM, preferably from 0.1-10 mM; the detergent is present in aconcentration from 0.001-1.0 wt %, preferably from 0.05-0.5 wt %,preferably from 0.02-0.2 wt %; and the divalent cation is present in theconcentration from 1-400 mM, preferably from 10-200 mM, more preferablyfrom 50-100 mM.
 17. The aqueous composition according to claim 16,further comprising a chaotropic agent in a concentration from 1 mM-1 M,preferably from 10 mM-200 mM.
 18. The aqueous composition according toclaim 1, wherein the pH is in the range from pH 2-12, preferably from pH5-10.
 19. The aqueous composition according to claim 1, furthercontaining Factor C protein, preferably recombinant Factor C protein.